mesh: Fix Friend node estalished

Since first poll request send by lpn use friend security
credentials, so, friend nodes should be able to decrypt with
friend security, even if they have not yet established a friendship.

This is port of 1b65fd066f66596177fbce2f60f0deb2697bb2cb

nimble/host/mesh/src/subnet.c

@@ -621,10 +621,6 @@ bool bt_mesh_net_cred_find(struct bt_mesh_net_rx *rx, struct os_mbuf *in,
 	for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
 		struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];
 
-		if (!frnd->established) {
-			continue;
-		}
-
 		if (!frnd->subnet) {
 			continue;
 		}