iproute2: ip-route.8.in: Add expires option for ip route

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>

man/man8/ip-route.8.in

@@ -132,7 +132,9 @@ replace " } "
 .B  congctl
 .IR NAME " ] [ "
 .B  pref
-.IR PREF " ]"
+.IR PREF " ] [ "
+.B  expires
+.IR TIME " ]"
 
 .ti -8
 .IR TYPE " := [ "
@@ -656,6 +658,12 @@ is a set of encapsulation attributes specific to the
 .in -8
 .RE
 
+.TP
+.BI expires " TIME " "(4.4+ only)"
+the route will be deleted after the expires time.
+.B Only
+support IPv6 at present.
+
 .TP
 ip route delete
 delete route