rbd: Use int type instead of time_t in public APIs

Updated the `LastSeen` property of MirrorPeerSite struct to be of int type instead
of `time_t` type.

Fixes: #870

Signed-off-by: Nikhil-Ladha <[email protected]>

rbd/mirror_peer_site.go

@@ -156,7 +156,7 @@ type MirrorPeerSite struct {
 	SiteName   string
 	MirrorUUID string
 	ClientName string
-	LastSeen   C.time_t
+	LastSeen   int
 }
 
 // ListMirrorPeerSite returns the list of peer sites