This change implements the SO_ERROR socket option that is used to obtain the last error reported by the network.

Squashed commit of the following:

Author: Gregory Nutt <gnutt@nuttx.org>

    net/: Trivial changes to PR from review.  Biggest difference:  type of s_error changed to int16_t to save a byte or two.

Author: liuhuahang <liuhuahang@xiaomi.com>

    Implement SO_ERROR for getsockopt()

net/socket/bind.c

@@ -159,7 +159,7 @@ int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen)
   ret = psock_bind(psock, addr, addrlen);
   if (ret < 0)
     {
-      set_errno(-ret);
+      _SO_SETERRNO(psock, -ret);
       return ERROR;
     }