BUG/MINOR: dns: server set by SRV records stay in "no resolution" status

This patch fixes a bug where some servers managed by SRV record query
types never ever recover from a "no resolution" status.
The problem is due to a wrong function called when breaking the
server/resolution (A/AAAA) relationship: this is performed when a server's SRV
record disappear from the SRV response.
diff --git a/include/proto/server.h b/include/proto/server.h
index d35a9c1..6663770 100644
--- a/include/proto/server.h
+++ b/include/proto/server.h
@@ -57,6 +57,7 @@
 int snr_resolution_cb(struct dns_requester *requester, struct dns_nameserver *nameserver);
 int snr_resolution_error_cb(struct dns_requester *requester, int error_code);
 struct server *snr_check_ip_callback(struct server *srv, void *ip, unsigned char *ip_family);
+void srv_free_from_resolution(struct server *srv);
 
 /* increase the number of cumulated connections on the designated server */
 static void inline srv_inc_sess_ctr(struct server *s)