bgpd: Check if as_type is not specified when peer is a peer-group member

Fixes this sequences:

```
neighbor pg4 peer-group
neighbor 127.0.0.4 peer-group pg4
neighbor 127.0.0.4 remote-as 65004

neighbor pg5 peer-group
neighbor 127.0.0.5 peer-group pg5
neighbor 127.0.0.5 remote-as internal
```

Fixes: 0dfe256 ("bgpd: Implement neighbor X remote-as auto")

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

bgpd/bgpd.c

@@ -2158,8 +2158,7 @@ int peer_remote_as(struct bgp *bgp, union sockunion *su, const char *conf_if,
 		/* When this peer is a member of peer-group.  */
 		if (peer->group) {
 			/* peer-group already has AS number/internal/external */
-			if (peer->group->conf->as
-			    || peer->group->conf->as_type) {
+			if (peer->group->conf->as || peer->group->conf->as_type != AS_UNSPECIFIED) {
 				/* Return peer group's AS number.  */
 				*as = peer->group->conf->as;
 				return BGP_ERR_PEER_GROUP_MEMBER;