MINOR: proxy: define PR_CAP_LB

Add a new proxy capability for proxy with load-balancing capabilities.
This help to differentiate listen/frontend/backend with special proxies
such as peer proxies.
diff --git a/include/haproxy/proxy-t.h b/include/haproxy/proxy-t.h
index 02d1391..95d3bc9 100644
--- a/include/haproxy/proxy-t.h
+++ b/include/haproxy/proxy-t.h
@@ -69,6 +69,7 @@
 #define PR_CAP_LISTEN  (PR_CAP_FE|PR_CAP_BE)
 #define PR_CAP_DEF     0x0004           /* defaults section */
 #define PR_CAP_LUA     0x0008           /* internal proxy used by lua engine */
+#define PR_CAP_LB      0x0010           /* load-balancing capabilities, i.e. listen/frontend/backend proxies */
 
 /* bits for proxy->options */
 #define PR_O_REDISP     0x00000001      /* allow reconnection to dispatch in case of errors */
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index 525da58..d5df78c 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -223,11 +223,11 @@
 	}
 
 	if (strcmp(args[0], "listen") == 0)
-		rc = PR_CAP_LISTEN;
+		rc = PR_CAP_LISTEN | PR_CAP_LB;
 	else if (strcmp(args[0], "frontend") == 0)
-		rc = PR_CAP_FE;
+		rc = PR_CAP_FE | PR_CAP_LB;
 	else if (strcmp(args[0], "backend") == 0)
-		rc = PR_CAP_BE;
+		rc = PR_CAP_BE | PR_CAP_LB;
 	else if (strcmp(args[0], "defaults") == 0) {
 		/* "defaults" must first delete the last no-name defaults if any */
 		proxy_destroy_defaults(proxy_find_by_name("", PR_CAP_DEF, 0));