extmod/modlwip: Fix error codes for duplicate calls to connect().

If socket is already connected, POSIX requires returning EISCONN. If
connection was requested, but not yet complete (for non-blocking
socket), error code is EALREADY.

http://pubs.opengroup.org/onlinepubs/7908799/xns/connect.html

extmod/modlwip.c

@@ -800,9 +800,9 @@ STATIC mp_obj_t lwip_socket_connect(mp_obj_t self_in, mp_obj_t addr_in) {
         case MOD_NETWORK_SOCK_STREAM: {
             if (socket->state != STATE_NEW) {
                 if (socket->state == STATE_CONNECTED) {
-                    mp_raise_OSError(MP_EALREADY);
+                    mp_raise_OSError(MP_EISCONN);
                 } else {
-                    mp_raise_OSError(MP_EINPROGRESS);
+                    mp_raise_OSError(MP_EALREADY);
                 }
             }
             // Register our receive callback.

py/mperrno.h

@@ -73,6 +73,7 @@
 #define MP_ECONNABORTED     (103) // Software caused connection abort
 #define MP_ECONNRESET       (104) // Connection reset by peer
 #define MP_ENOBUFS          (105) // No buffer space available
+#define MP_EISCONN          (106) // Transport endpoint is already connected
 #define MP_ENOTCONN         (107) // Transport endpoint is not connected
 #define MP_ETIMEDOUT        (110) // Connection timed out
 #define MP_ECONNREFUSED     (111) // Connection refused
@@ -127,6 +128,7 @@
 #define MP_ECONNABORTED     ECONNABORTED
 #define MP_ECONNRESET       ECONNRESET
 #define MP_ENOBUFS          ENOBUFS
+#define MP_EISCONN          EISCONN
 #define MP_ENOTCONN         ENOTCONN
 #define MP_ETIMEDOUT        ETIMEDOUT
 #define MP_ECONNREFUSED     ECONNREFUSED