net: sockets: packet: Allow proto 0 for RAW sockets

According to AF_PACKET man pages protocol number 0 is allowed, however
in such case the socket is only capable of transmitting packets then:

  "If protocol is set to zero, no packets are received."

Therefore, allow to create sockets with such protocol, and at the
connection.c level filter out such sockets from data reception.

Signed-off-by: Robert Lubos <[email protected]>

Author: rlubos

subsys/net/ip/connection.c

@@ -793,7 +793,7 @@ enum net_verdict net_conn_input(struct net_pkt *pkt,
 			 * case.
 			 */
 			if (IS_ENABLED(CONFIG_NET_SOCKETS_PACKET) && pkt_family == AF_PACKET) {
-				if (proto != ETH_P_ALL) {
+				if (conn->proto == 0 || proto != ETH_P_ALL) {
 					continue; /* wrong protocol */
 				}
 			} else if (IS_ENABLED(CONFIG_NET_SOCKETS_INET_RAW) && raw_ip_pkt) {

subsys/net/lib/sockets/sockets_packet.c

@@ -486,7 +486,8 @@ static bool packet_is_supported(int family, int type, int proto)
 	switch (type) {
 	case SOCK_RAW:
 		proto = ntohs(proto);
-		return proto == ETH_P_ALL
+		return proto == 0
+		  || proto == ETH_P_ALL
 		  || proto == ETH_P_ECAT
 		  || proto == ETH_P_IEEE802154;