res_pjsip_session: sdp group:BUNDLE attribute being truncated

When setting/appending the media id's to the bundle group attribute a '-1' was
being passed to the 'ast_str_set/append' function for the 'max_len' parameter.
This essentially capped the length of the string to what it was originally
allocated with. In this case 64 bytes.

This patch makes it so a '0' is passed as in for the 'max_len', which means
"no maximum length".

ASTERISK-27955 #close

Change-Id: Iec565df6600401d54a502854a53d19bb4cc34876

res/res_pjsip_session.c

@@ -3847,14 +3847,14 @@ static int add_bundle_groups(struct ast_sip_session *session, pj_pool_t *pool, p
 				continue;
 			}
 
-			ast_str_set(&bundle_group->attr_string, -1, "BUNDLE %s", session_media->mid);
+			ast_str_set(&bundle_group->attr_string, 0, "BUNDLE %s", session_media->mid);
 			continue;
 		}
 
 		for (mid_id = 1; mid_id < PJMEDIA_MAX_SDP_MEDIA; ++mid_id) {
 			if (!bundle_group->mids[mid_id]) {
 				bundle_group->mids[mid_id] = session_media->mid;
-				ast_str_append(&bundle_group->attr_string, -1, " %s", session_media->mid);
+				ast_str_append(&bundle_group->attr_string, 0, " %s", session_media->mid);
 				break;
 			} else if (!strcmp(bundle_group->mids[mid_id], session_media->mid)) {
 				break;