vrrp: don't log netlink errors when removing routes that may not exist

When keepalived starts up it removes and VRRP instance virtual_routes
in case they were left over from a previous run of keepalived. This
commit stops keepalived logging netlink errors if the routes don't
exist.

Similarly when an interface goes down, keepalived attempts to remove
any virtual routes, but the kernel may have already removed the
routes, so also don't log any errors.

Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>