It is not always necessary to add a host route for the gre peer address.
This introduces a new config option 'nohostroute' (similar to the
option introduced for wireguard in d8e2e19) to allow to disable
the creation of those routes explicitely.
This is a backport from OpenWrt master.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>
