[NET]: Make sure sockets implement splice_read

Fixes a segmentation fault when trying to splice from a non-TCP socket.

Signed-off-by: Rémi Denis-Courmont <rdenis@simphalempin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/socket.c b/net/socket.c
index 7651de0..b6d35cd 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -701,6 +701,9 @@
 {
 	struct socket *sock = file->private_data;
 
+	if (unlikely(!sock->ops->splice_read))
+		return -EINVAL;
+
 	return sock->ops->splice_read(sock, ppos, pipe, len, flags);
 }