fix wifinina UDP send

Fix an error I introduced in porting wifinina to netdev.  The driver was
starting a client on the socket once, during Connect.  The first UDP
send on the socket would succeed, any subsequent sends would fail.  The
fix is to start the client on the socket for each UDP send.

I think I see the logic in this design, so the fix makes sense.  If the
device was sending to many UDP clients, it could use a single socket,
but change the dst addr for each send.  The pkt data would be queued to
hw just once, and then sent from hw to each client dst addr.  This would
be a real efficient way to multicast to many clients.

wifinina/wifinina.go

@@ -165,7 +165,8 @@ type hwerr uint8
 
 type socket struct {
 	protocol int
-	ip       netip.AddrPort
+	laddr    netip.AddrPort // Set in Bind()
+	raddr    netip.AddrPort // Set in Connect()
 	inuse    bool
 }
 
@@ -603,7 +604,7 @@ func (w *wifinina) Bind(sockfd int, ip netip.AddrPort) error {
 		w.startServer(sock, ip.Port(), protoModeUDP)
 	}
 
-	socket.ip = ip
+	socket.laddr = ip
 
 	return nil
 }
@@ -638,7 +639,8 @@ func (w *wifinina) Connect(sockfd int, host string, ip netip.AddrPort) error {
 	case netdev.IPPROTO_TLS:
 		w.startClient(sock, host, 0, ip.Port(), protoModeTLS)
 	case netdev.IPPROTO_UDP:
-		w.startClient(sock, "", toUint32(ip.Addr().As4()), ip.Port(), protoModeUDP)
+		// See start in sendUDP()
+		socket.raddr = ip
 		return nil
 	}
 
@@ -667,7 +669,7 @@ func (w *wifinina) Listen(sockfd int, backlog int) error {
 
 	switch socket.protocol {
 	case netdev.IPPROTO_TCP:
-		w.startServer(sock, socket.ip.Port(), protoModeTCP)
+		w.startServer(sock, socket.laddr.Port(), protoModeTCP)
 	case netdev.IPPROTO_UDP:
 	default:
 		return netdev.ErrProtocolNotSupported
@@ -794,7 +796,10 @@ func (w *wifinina) sendTCP(sock sock, buf []byte, deadline time.Time) (int, erro
 	return -1, netdev.ErrTimeout
 }
 
-func (w *wifinina) sendUDP(sock sock, buf []byte, deadline time.Time) (int, error) {
+func (w *wifinina) sendUDP(sock sock, raddr netip.AddrPort, buf []byte, deadline time.Time) (int, error) {
+
+	// Start a client for each send
+	w.startClient(sock, "", toUint32(raddr.Addr().As4()), raddr.Port(), protoModeUDP)
 
 	// Queue it
 	ok := w.insertDataBuf(sock, buf)
@@ -826,7 +831,7 @@ func (w *wifinina) sendChunk(sockfd int, buf []byte, deadline time.Time) (int, e
 	case netdev.IPPROTO_TCP, netdev.IPPROTO_TLS:
 		return w.sendTCP(sock, buf, deadline)
 	case netdev.IPPROTO_UDP:
-		return w.sendUDP(sock, buf, deadline)
+		return w.sendUDP(sock, socket.raddr, buf, deadline)
 	}
 
 	return -1, netdev.ErrProtocolNotSupported