net: Make sock protocol value checks more specific

SK_PROTOCOL_MAX is only used in two places, for DECNet and AX.25. The
limits have more to do with the those protocol definitions than they do
with the data type of sk_protocol, so remove SK_PROTOCOL_MAX and use
U8_MAX directly.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sock.h b/include/net/sock.h
index 8dff68b..091e554 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -458,7 +458,6 @@ struct sock {
 				sk_userlocks : 4,
 				sk_protocol  : 8,
 				sk_type      : 16;
-#define SK_PROTOCOL_MAX U8_MAX
 	u16			sk_gso_max_segs;
 	u8			sk_pacing_shift;
 	unsigned long	        sk_lingertime;
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 324306d..ff57ea8 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -808,7 +808,7 @@ static int ax25_create(struct net *net, struct socket *sock, int protocol,
 	struct sock *sk;
 	ax25_cb *ax25;
 
-	if (protocol < 0 || protocol > SK_PROTOCOL_MAX)
+	if (protocol < 0 || protocol > U8_MAX)
 		return -EINVAL;
 
 	if (!net_eq(net, &init_net))
diff --git a/net/decnet/af_decnet.c b/net/decnet/af_decnet.c
index e19a92a..0a46ea3 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -670,7 +670,7 @@ static int dn_create(struct net *net, struct socket *sock, int protocol,
 {
 	struct sock *sk;
 
-	if (protocol < 0 || protocol > SK_PROTOCOL_MAX)
+	if (protocol < 0 || protocol > U8_MAX)
 		return -EINVAL;
 
 	if (!net_eq(net, &init_net))