MEDIUM: server: support {check,agent}_addr, agent_port in server state

logical followup from cli commands addition, so that the state server
file stays compatible with the changes made at runtime; use previously
added helper to load server attributes.

also alloc a specific chunk to avoid mixing with other called functions
using it

Signed-off-by: William Dauchy <wdauchy@gmail.com>
diff --git a/doc/management.txt b/doc/management.txt
index 423c614..60e25c7 100644
--- a/doc/management.txt
+++ b/doc/management.txt
@@ -2455,7 +2455,10 @@
      srv_port:                    Server port.
      srvrecord:                   DNS SRV record associated to this SRV.
      srv_use_ssl:                 use ssl for server connections.
-     srv_check_port:              Server check port.
+     srv_check_port:              Server health check port.
+     srv_check_addr:              Server health check address.
+     srv_agent_addr:              Server health agent address.
+     srv_agent_port:              Server health agent port.
 
 show sess
   Dump all known sessions. Avoid doing this on slow connections as this can