BUG/MAJOR: can't enable a server through the stat socket

When a server is disabled in the configuration using the "disabled"
keyword, a single flag is positionned: SRV_ADMF_CMAINT (use to be
SRV_ADMF_FMAINT)..
That said, when providing the first version of this code, we also
changed the SRV_ADMF_MAINT mask to match any of the possible MAINT
cases: SRV_ADMF_FMAINT, SRV_ADMF_IMAINT, SRV_ADMF_CMAINT

Since SRV_ADMF_CMAINT is never (and is not supposed to be) altered at
run time, once a server has this flag set up, it can never ever be
enabled again using the stats socket.

In order to fix this, we should:
- consider SRV_ADMF_CMAINT as a simple flag to report the state in the
  old configuration file (will be used after a reload to deduce the
  state of the server in a new running process)
- enabling both SRV_ADMF_CMAINT and SRV_ADMF_FMAINT when the keyword
  "disabled" is in use in the configuration
- update the mask SRV_ADMF_MAINT as it was before, to only match
  SRV_ADMF_FMAINT and SRV_ADMF_IMAINT.

The following patch perform the changes above.
It allows fixing the regression without breaking the way the up coming
feature (seamless server state accross reloads) is going to work.

Note: this is 1.6-only, no backport needed.
diff --git a/include/types/server.h b/include/types/server.h
index ee31794..40b8308 100644
--- a/include/types/server.h
+++ b/include/types/server.h
@@ -75,8 +75,8 @@
 enum srv_admin {
 	SRV_ADMF_FMAINT    = 0x01,        /* the server was explicitly forced into maintenance */
 	SRV_ADMF_IMAINT    = 0x02,        /* the server has inherited the maintenance status from a tracked server */
+	SRV_ADMF_MAINT     = 0x03,        /* mask to check if any maintenance flag is present */
 	SRV_ADMF_CMAINT    = 0x04,        /* the server is in maintenance because of the configuration */
-	SRV_ADMF_MAINT     = 0x07,        /* mask to check if any maintenance flag is present */
 	SRV_ADMF_FDRAIN    = 0x08,        /* the server was explicitly forced into drain state */
 	SRV_ADMF_IDRAIN    = 0x10,        /* the server has inherited the drain status from a tracked server */
 	SRV_ADMF_DRAIN     = 0x18,        /* mask to check if any drain flag is present */