Remove explicit enum from protocol structures

Explicit 'enum' keyword does not work with portablexdr-rpcgeb, causing its
parser to fail. Fix method is borrowed from virnetprotocol.x

Signed-off-by: Pavel Fedin <p.fedin@samsung.com>

src/lxc/lxc_monitor_protocol.x

@@ -30,7 +30,7 @@ enum virLXCMonitorExitStatus {
 };
 
 struct virLXCMonitorExitEventMsg {
-    enum virLXCMonitorExitStatus status;
+    virLXCMonitorExitStatus status;
 };
 
 struct virLXCMonitorInitEventMsg {

src/lxc_monitor_protocol-structs

@@ -5,7 +5,7 @@ enum virLXCMonitorExitStatus {
         VIR_LXC_MONITOR_EXIT_STATUS_REBOOT = 2,
 };
 struct virLXCMonitorExitEventMsg {
-        enum virLXCMonitorExitStatus status;
+        virLXCMonitorExitStatus    status;
 };
 struct virLXCMonitorInitEventMsg {
         uint64_t                   initpid;