extmod/modlwip: Add ioctl method to socket, with poll implementation.

Implementation of polling may need further fine tuning, but basic
functionality works (tested on esp8266).

extmod/modlwip.c

@@ -1127,6 +1127,34 @@ STATIC mp_uint_t lwip_socket_write(mp_obj_t self_in, const void *buf, mp_uint_t
     return MP_STREAM_ERROR;
 }
 
+STATIC mp_uint_t lwip_socket_ioctl(mp_obj_t self_in, mp_uint_t request, uintptr_t arg, int *errcode) {
+    lwip_socket_obj_t *socket = self_in;
+    mp_uint_t ret;
+
+    if (request == MP_STREAM_POLL) {
+        uintptr_t flags = arg;
+        ret = 0;
+
+        if (flags & MP_STREAM_POLL_RD && socket->incoming.pbuf != NULL) {
+            ret |= MP_STREAM_POLL_RD;
+        }
+
+        if (flags & MP_STREAM_POLL_WR && tcp_sndbuf(socket->pcb.tcp) > 0) {
+            ret |= MP_STREAM_POLL_WR;
+        }
+
+        if (flags & MP_STREAM_POLL_HUP && socket->state == STATE_PEER_CLOSED) {
+            ret |= MP_STREAM_POLL_HUP;
+        }
+
+    } else {
+        *errcode = MP_EINVAL;
+        ret = MP_STREAM_ERROR;
+    }
+
+    return ret;
+}
+
 STATIC const mp_map_elem_t lwip_socket_locals_dict_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR___del__), (mp_obj_t)&lwip_socket_close_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_close), (mp_obj_t)&lwip_socket_close_obj },
@@ -1153,6 +1181,7 @@ STATIC MP_DEFINE_CONST_DICT(lwip_socket_locals_dict, lwip_socket_locals_dict_tab
 STATIC const mp_stream_p_t lwip_socket_stream_p = {
     .read = lwip_socket_read,
     .write = lwip_socket_write,
+    .ioctl = lwip_socket_ioctl,
 };
 
 STATIC const mp_obj_type_t lwip_socket_type = {