sock: Allow flushing even if the socket is in a poll group

If we call flush, we want to flush regardless of whether there is a poll
group.

Change-Id: I88680105d999a909f3f1fe75be9caff31a8555ff
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16420
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>

lib/sock/sock.c

@@ -520,11 +520,6 @@ spdk_sock_flush(struct spdk_sock *sock)
 		return -1;
 	}
 
-	/* Sock is in a polling group, so group polling mechanism will work */
-	if (sock->group_impl != NULL) {
-		return 0;
-	}
-
 	return sock->net_impl->flush(sock);
 }