MINOR: fd: don't report maxfd in alert messages

The listeners and connectors may complain that process-wide or
system-wide FD limits have been reached and will in this case report
maxfd as the limit. This is wrong in fact since there's no reason for
the whole FD space to be contiguous when the total # of FD is reached.
A better approach would consist in reporting the accurate number of
opened FDs, but this is pointless as what matters here is to give a
hint about what might be wrong. So let's simply report the configured
maxsock, which will generally explain why the process' limits were
reached, which is the most common reason. This removes another
dependency on maxfd.
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index 1579dd0..754acd2 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -452,20 +452,20 @@
 		if (errno == ENFILE) {
 			conn->err_code = CO_ER_SYS_FDLIM;
 			send_log(be, LOG_EMERG,
-				 "Proxy %s reached system FD limit at %d. Please check system tunables.\n",
-				 be->id, maxfd);
+				 "Proxy %s reached system FD limit (maxsock=%d). Please check system tunables.\n",
+				 be->id, global.maxsock);
 		}
 		else if (errno == EMFILE) {
 			conn->err_code = CO_ER_PROC_FDLIM;
 			send_log(be, LOG_EMERG,
-				 "Proxy %s reached process FD limit at %d. Please check 'ulimit-n' and restart.\n",
-				 be->id, maxfd);
+				 "Proxy %s reached process FD limit (maxsock=%d). Please check 'ulimit-n' and restart.\n",
+				 be->id, global.maxsock);
 		}
 		else if (errno == ENOBUFS || errno == ENOMEM) {
 			conn->err_code = CO_ER_SYS_MEMLIM;
 			send_log(be, LOG_EMERG,
-				 "Proxy %s reached system memory limit at %d sockets. Please check system tunables.\n",
-				 be->id, maxfd);
+				 "Proxy %s reached system memory limit (maxsock=%d). Please check system tunables.\n",
+				 be->id, global.maxsock);
 		}
 		else if (errno == EAFNOSUPPORT || errno == EPROTONOSUPPORT) {
 			conn->err_code = CO_ER_NOPROTO;