net/inet: Only setup poll for UDP when s_type == SOCK_DGRAM

Problem:
A SOCK_CTRL socket may be led to udp_pollsetup but never reaches
udp_pollteardown, it seems that we shouldn't call udp_pollsetup for
other socket types.

Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>

net/inet/inet_sockif.c

@@ -1503,7 +1503,7 @@ static inline int inet_pollsetup(FAR struct socket *psock,
   else
 #endif /* NET_TCP_HAVE_STACK */
 #ifdef NET_UDP_HAVE_STACK
-  if (psock->s_type != SOCK_STREAM)
+  if (psock->s_type == SOCK_DGRAM)
     {
       return udp_pollsetup(psock, fds);
     }