BUG/MINOR: stats: fixing stat shows disabled frontend status as 'OPEN'

This patch adresses the issue #1626.

Adding support for PR_FL_PAUSED flag in the function stats_fill_fe_stats().
The command 'show stat' now properly reports a disabled frontend
using "PAUSED" state label.

This patch depends on the following commits:
  - 7d00077fd5 "BUG/MEDIUM: proxy: ensure pause_proxy()
  and resume_proxy() own PROXY_LOCK".
  - 001328873c "MINOR: listener: small API change"
  - d46f437de6 "MINOR: proxy/listener: support for additional PAUSED state"

It should be backported to 2.6, 2.5 and 2.4
diff --git a/src/stats.c b/src/stats.c
index fdbca00..97e7fd8 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -1697,9 +1697,18 @@
 			case ST_F_DSES:
 				metric = mkf_u64(FN_COUNTER, px->fe_counters.denied_sess);
 				break;
-			case ST_F_STATUS:
-				metric = mkf_str(FO_STATUS, (px->flags & (PR_FL_DISABLED|PR_FL_STOPPED)) ? "STOP" : "OPEN");
+			case ST_F_STATUS: {
+				const char *state;
+
+				if (px->flags & (PR_FL_DISABLED|PR_FL_STOPPED))
+					state = "STOP";
+				else if (px->flags & PR_FL_PAUSED)
+					state = "PAUSED";
+				else
+					state = "OPEN";
+				metric = mkf_str(FO_STATUS, state);
 				break;
+			}
 			case ST_F_PID:
 				metric = mkf_u32(FO_KEY, 1);
 				break;