Add two helper functions, one for IPv4 and one for IPv6, to ensure
that the core code benefits from compiler type checking when adding
routes. Previously nm_netlink_route_add() took a void* which meant
we messed up adding IPv6 routes sometimes due to confusion over
what was supposed to be passed to it. Also fixes what appears to
be a C&P error with add_ip6_route_to_gateway().
Reported by Tomáš Trnka <tomastrnka@gmx.com>
Callers of this function have a better idea of they want to
log errors or not. Let them handle it, since they already
do, and having a warning here was causing duplicate log
messages.
Flags are not getting set when a route is added (e.g. NLM_F_REPLACE).
Apparently this was fixed in Ubuntu, but I didn't see a patch here, so
here it is.
