BSD: Ensure process creation timestamp is init'd

While BSDs don't support process creation timestamp information via
PEERCRED for Unix sockets, we need to actually initialize the value
because it is used by the libvirt code.

src/rpc/virnetsocket.c

@@ -1153,7 +1153,7 @@ int virNetSocketGetUNIXIdentity(virNetSocketPtr sock,
                                 uid_t *uid,
                                 gid_t *gid,
                                 pid_t *pid,
-                                unsigned long long *timestamp ATTRIBUTE_UNUSED)
+                                unsigned long long *timestamp)
 {
     struct xucred cr;
     socklen_t cr_len = sizeof(cr);
@@ -1178,7 +1178,9 @@ int virNetSocketGetUNIXIdentity(virNetSocketPtr sock,
         return -1;
     }
 
+    /* PID and process creation time are not supported on BSDs */
     *pid = -1;
+    *timestamp = -1;
     *uid = cr.cr_uid;
     *gid = cr.cr_gid;