sunrpc: Fix return value of get_srcport()

Since bc1c56e9 transport->srcport may by unset, causing
get_srcport() to return 0 when called. Fix this by querying the port
from the underlying socket instead of the transport.

Fixes: bc1c56e9 (SUNRPC: prevent port reuse on transports which don't request it)
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtsock.c

@@ -1656,7 +1656,7 @@ static int xs_get_srcport(struct sock_xprt *transport)
 unsigned short get_srcport(struct rpc_xprt *xprt)
 {
 	struct sock_xprt *sock = container_of(xprt, struct sock_xprt, xprt);
-	return sock->srcport;
+	return xs_sock_getport(sock->sock);
 }
 EXPORT_SYMBOL(get_srcport);