Allow route change requests to not specify the gateway.

Only require a gateway to be specified on a route add request.  On
a route change request that does not specify the gateway, the
gateway will remain the same.  This allows changing other route
parameters without having to re-specifying the gateway, like in
"route change 10.0.0.0/8 -mtu 9000".

Update the route(8) manpage to explicitly call out this usage
as being supported.

MFC after: 2 weeks
Sponsored by: Dell EMC Isilon
Reviewed By: eugen (rtsock.c change), rgrimes
Differential Revision: https://reviews.freebsd.org/D14291

1 files changed, 15 insertions, 3 deletions

diff --git a/sbin/route/route.8 b/sbin/route/route.8
index 692e1a891936..34af296247a6 100644
--- a/sbin/route/route.8
+++ b/sbin/route/route.8
@@ -28,7 +28,7 @@
 .\"     @(#)route.8	8.3 (Berkeley) 3/19/94
 .\" $FreeBSD$
 .\"
-.Dd November 11, 2014
+.Dd February 16, 2018
 .Dt ROUTE 8
 .Os
 .Sh NAME
@@ -164,18 +164,30 @@ option is specified, the operation will be applied to
 the specified FIB
 .Pq routing table .
 .Pp
-The other commands have the following syntax:
+The add command has the following syntax:
 .Pp
 .Bd -ragged -offset indent -compact
 .Nm
 .Op Fl n
-.Ar command
+.Cm add
 .Op Fl net No \&| Fl host
 .Ar destination gateway
 .Op Ar netmask
 .Op Fl fib Ar number
 .Ed
 .Pp
+and the other commands have the following syntax:
+.Pp
+.Bd -ragged -offset indent -compact
+.Nm
+.Op Fl n
+.Ar command
+.Op Fl net No \&| Fl host
+.Ar destination
+.Op Ar gateway Op Ar netmask
+.Op Fl fib Ar number
+.Ed
+.Pp
 where
 .Ar destination
 is the destination host or network,