net: mctp: remove routes by netid, not by device

In upcoming changes, a route may not have a device associated. Since the
route is matched on the (network, eid) tuple, pass the netid itself into
mctp_route_remove.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20250702-dev-forwarding-v5-11-1468191da8a4@codeconstruct.com.au


Signed-off-by: Paolo Abeni <pabeni@redhat.com>