Add network device driver model, netdev

This PR adds a network device driver model called netdev. There will be a companion PR for TinyGo drivers to update the netdev drivers and network examples. This PR covers the core "net" package.

An RFC for the work is here: #tinygo-org/drivers#487. Some things have changed from the RFC, but nothing major.

The "net" package is a partial port of Go's "net" package, version 1.19.3. The src/net/README file has details on what is modified from Go's "net" package.

Most "net" features are working as they would in normal Go. TCP/UDP/TLS protocol support is there. As well as HTTP client and server support. Standard Go network packages such as golang.org/x/net/websockets and Paho MQTT client work as-is. Other packages are likely to work as-is.

Testing results are here (https://docs.google.com/spreadsheets/d/e/2PACX-1vT0cCjBvwXf9HJf6aJV2Sw198F2ief02gmbMV0sQocKT4y4RpfKv3dh6Jyew8lQW64FouZ8GwA2yjxI/pubhtml?gid=1013173032&single=true).

tlssock.go

@@ -0,0 +1,154 @@
+// TINYGO: The following is copied and modified from Go 1.19.3 official implementation.
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TLS low level connection and record layer
+
+package net
+
+import (
+	"fmt"
+	"strconv"
+	"syscall"
+	"time"
+)
+
+func DialTLS(addr string) (*TLSConn, error) {
+
+	host, sport, err := SplitHostPort(addr)
+	if err != nil {
+		return nil, err
+	}
+
+	port, err := strconv.Atoi(sport)
+	if err != nil {
+		return nil, err
+	}
+
+	if port == 0 {
+		port = 443
+	}
+
+	fd, err := netdev.Socket(syscall.AF_INET, syscall.SOCK_STREAM, syscall.IPPROTO_TLS)
+	if err != nil {
+		return nil, err
+	}
+
+	if err = netdev.Connect(fd, host, IP{}, port); err != nil {
+		netdev.Close(fd)
+		return nil, err
+	}
+
+	return &TLSConn{
+		fd: fd,
+	}, nil
+}
+
+// A TLSConn represents a secured connection.
+// It implements the net.Conn interface.
+type TLSConn struct {
+	fd            int
+	readDeadline  time.Time
+	writeDeadline time.Time
+}
+
+// Access to net.Conn methods.
+// Cannot just embed net.Conn because that would
+// export the struct field too.
+
+// LocalAddr returns the local network address.
+func (c *TLSConn) LocalAddr() Addr {
+	// TODO
+	return nil
+}
+
+// RemoteAddr returns the remote network address.
+func (c *TLSConn) RemoteAddr() Addr {
+	// TODO
+	return nil
+}
+
+// SetDeadline sets the read and write deadlines associated with the connection.
+// A zero value for t means Read and Write will not time out.
+// After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
+func (c *TLSConn) SetDeadline(t time.Time) error {
+	c.readDeadline = t
+	c.writeDeadline = t
+	return nil
+}
+
+// SetReadDeadline sets the read deadline on the underlying connection.
+// A zero value for t means Read will not time out.
+func (c *TLSConn) SetReadDeadline(t time.Time) error {
+	c.readDeadline = t
+	return nil
+}
+
+// SetWriteDeadline sets the write deadline on the underlying connection.
+// A zero value for t means Write will not time out.
+// After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
+func (c *TLSConn) SetWriteDeadline(t time.Time) error {
+	c.writeDeadline = t
+	return nil
+}
+
+func (c *TLSConn) Read(b []byte) (int, error) {
+	var timeout time.Duration
+
+	now := time.Now()
+
+	if !c.readDeadline.IsZero() {
+		if c.readDeadline.Before(now) {
+			return 0, fmt.Errorf("Read deadline expired")
+		} else {
+			timeout = c.readDeadline.Sub(now)
+		}
+	}
+
+	n, err := netdev.Recv(c.fd, b, 0, timeout)
+	// Turn the -1 socket error into 0 and let err speak for error
+	if n < 0 {
+		n = 0
+	}
+	return n, err
+}
+
+func (c *TLSConn) Write(b []byte) (int, error) {
+	var timeout time.Duration
+
+	now := time.Now()
+
+	if !c.writeDeadline.IsZero() {
+		if c.writeDeadline.Before(now) {
+			return 0, fmt.Errorf("Write deadline expired")
+		} else {
+			timeout = c.writeDeadline.Sub(now)
+		}
+	}
+
+	n, err := netdev.Send(c.fd, b, 0, timeout)
+	// Turn the -1 socket error into 0 and let err speak for error
+	if n < 0 {
+		n = 0
+	}
+	return n, err
+}
+
+func (c *TLSConn) Close() error {
+	return netdev.Close(c.fd)
+}
+
+// Handshake runs the client or server handshake
+// protocol if it has not yet been run.
+//
+// Most uses of this package need not call Handshake explicitly: the
+// first Read or Write will call it automatically.
+//
+// For control over canceling or setting a timeout on a handshake, use
+// HandshakeContext or the Dialer's DialContext method instead.
+func (c *TLSConn) Handshake() error {
+	panic("TLSConn.Handshake() not implemented")
+	return nil
+}