net: guard tcp_set_keepalive() to tcp sockets

Its possible to use RAW sockets to get a crash in
tcp_set_keepalive() / sk_reset_timer()

Fix is to make sure socket is a SOCK_STREAM one.
Reported-by: NDave Jones <davej@redhat.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -691,7 +691,8 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 
 	case SO_KEEPALIVE:
 #ifdef CONFIG_INET
-		if (sk->sk_protocol == IPPROTO_TCP)
+		if (sk->sk_protocol == IPPROTO_TCP &&
+		    sk->sk_type == SOCK_STREAM)
 			tcp_set_keepalive(sk, valbool);
 #endif
 		sock_valbool_flag(sk, SOCK_KEEPOPEN, valbool);