BUG/MINOR: server: make sure "show servers state" hides private bits

In the past we've seen "show servers state" dump some internal bits for
the check states, that were causing regtests to fail. The relevant bits
have been added to the doc to fix the public API and make sure they do
not change by accident, but the output doesn't take care of masking the
undesired ones, causing regtests (and possibly user programs) to fail
when new bits are added. Let's add the mask for the only documented ones
(0x0F for check and 0x1F for agent respectively).

This could be backported wherever the server state is present, though
there's a tiny risk that some undocumented bits might have already
leaked to some user scripts, so it might be wise to wait a bit before
doing that or even not to backport too far.

src/proxy.c

@@ -2795,7 +2795,7 @@ static int dump_servers_state(struct stconn *sc)
 			             srv->cur_state, srv->cur_admin, srv->uweight, srv->iweight,
 				     (long int)srv_time_since_last_change,
 			             srv->check.status, srv->check.result, srv->check.health,
-				     srv->check.state, srv->agent.state,
+				     srv->check.state & 0x0F, srv->agent.state & 0x1F,
 			             bk_f_forced_id, srv_f_forced_id,
 				     srv->hostname ? HA_ANON_CLI(srv->hostname) : "-", srv->svc_port,
 			             srvrecord ? srvrecord : "-", srv->use_ssl, srv->check.port,