move netdev and netlink into their own packages and out of drivers

This moves the netdev/netlink namespace out of drivers and into their
own packages.  Also, defines netdev and netlink as L3/L4 and L2 OSI
layers, respectively.  Move some L3 functionality from netlink to
netdev (GetIPAddr).

For netlink, add ConnectParams for NetConnect to pass in L2 connection
parameters (ssid, pass, auth_type, etc).  Also adds connection mode
(STA, AP, etc).

For netlink, add SendEth and RecvEthFunc funcs to handle L2 send/recv of
Ethernet pkts.

netlink/netlink.go

@@ -0,0 +1,103 @@
+// L2 data link layer
+
+package netlink
+
+import (
+	"errors"
+	"net"
+	"time"
+)
+
+var (
+	ErrConnected         = errors.New("Already connected")
+	ErrConnectFailed     = errors.New("Connect failed")
+	ErrConnectTimeout    = errors.New("Connect timed out")
+	ErrMissingSSID       = errors.New("Missing WiFi SSID")
+	ErrAuthTypeNoGood    = errors.New("Wifi authorization type not supported")
+	ErrConnectModeNoGood = errors.New("Connect mode not supported")
+	ErrNotSupported      = errors.New("Not supported")
+)
+
+type Event int
+
+// Network events
+const (
+	// The device's network connection is now UP
+	EventNetUp Event = iota
+	// The device's network connection is now DOWN
+	EventNetDown
+)
+
+type ConnectMode int
+
+// Connect modes
+const (
+	ConnectModeSTA = iota // Connect as Wifi station (default)
+	ConnectModeAP         // Connect as Wifi Access Point
+)
+
+type AuthType int
+
+// Wifi authorization types.  Used when setting up an access point, or
+// connecting to an access point
+const (
+	AuthTypeWPA2      = iota // WPA2 authorization (default)
+	AuthTypeOpen             // No authorization required (open)
+	AuthTypeWPA              // WPA authorization
+	AuthTypeWPA2Mixed        // WPA2/WPA mixed authorization
+)
+
+const DefaultConnectTimeout = 10 * time.Second
+
+type ConnectParams struct {
+	// Connect mode
+	ConnectMode
+	// SSID of Wifi AP
+	Ssid string
+	// Passphrase of Wifi AP
+	Passphrase string
+	// Wifi authorization type
+	AuthType
+	// Wifi country code as two-char string.  E.g. "XX" for world-wide,
+	// "US" for USA, etc.
+	Country string
+
+	// Retries is how many attempts to connect before returning with a
+	// "Connect failed" error.  Zero means infinite retries.
+	Retries int
+
+	// Timeout duration for each connection attempt.  The default zero
+	// value means 10sec.
+	ConnectTimeout time.Duration
+
+	// Watchdog ticker duration.  On tick, the watchdog will check for
+	// downed connection or hardware fault and try to recover the
+	// connection.  Set to zero to disable watchodog.
+	WatchdogTimeout time.Duration
+}
+
+// Netlinker is TinyGo's OSI L2 data link layer interface.  Network device
+// drivers implement Netlinker to expose the device's L2 functionality.
+
+type Netlinker interface {
+
+	// Connect device to network
+	NetConnect(params *ConnectParams) error
+
+	// Disconnect device from network
+	NetDisconnect()
+
+	// Notify to register callback for network events
+	NetNotify(cb func(Event))
+
+	// GetHardwareAddr returns device MAC address
+	GetHardwareAddr() (net.HardwareAddr, error)
+
+	// SendEth sends an Ethernet packet
+	// TODO describe content of pkt
+	SendEth(pkt []byte) error
+
+	// RecvEth callback function for receiving Ethernet pkt
+	// TODO describe content of pkt
+	RecvEthFunc(func(pkt []byte) error)
+}