[nrf fromlist] bluetooth: mesh: lpn shouldn't relay messages received over friendship

Commit fixes the issue when lpn device relays
broad- and group cast messages received over
friendship queue. This is specification violation,
see Table 3.13: Network layer Network PDU retransmission
requirements. Also, it does not have sense since
sending messages have already happened and lpn
just consumes extra power to retransmit useless data.
In general, lpn device will be more power efficient after
this fix.

Upstream PR #: 100285

Signed-off-by: Aleksandr Khromykh <[email protected]>
(cherry picked from commit b502dec131912d546de6e0e570bcb1aaf7c001e9)
(cherry picked from commit 66cda9d)

Author: alxelax

subsys/bluetooth/mesh/net.c

@@ -924,10 +924,13 @@ void bt_mesh_net_recv(struct net_buf_simple *data, int8_t rssi,
 	}
 
 	/* Relay if this was a group/virtual address, or if the destination
-	 * was neither a local element nor an LPN we're Friends for.
+	 * was neither a local element nor an LPN we're Friends for, and
+	 * device is not in Friendship as the Low Power node or the message is not encrypted using
+	 * friendship security credentials.
 	 */
-	if (!BT_MESH_ADDR_IS_UNICAST(rx.ctx.recv_dst) ||
-	    (!rx.local_match && !rx.friend_match)) {
+	if ((!BT_MESH_ADDR_IS_UNICAST(rx.ctx.recv_dst) ||
+	    (!rx.local_match && !rx.friend_match)) &&
+	    (!bt_mesh_lpn_established() || !rx.friend_cred)) {
 		net_buf_simple_restore(&buf, &state);
 		bt_mesh_net_relay(&buf, &rx, false);
 	}