Fix up default route selection by
a) Forcing user to explicitly chose 'dhcp' as a mechanism for
specifying a default route, rather than guessing based on one or more
interfaces being configured by dhcp.
b) If the user specified default route does not work, re-present the
existing default route rather than losing it.
c) Move default route selection to after nameserver activation so the
user can specify a hostname as the default route.
Change /etc/netstart so that /etc/mygate wins if a default route was
already specified (i.e. by dhcp).
ok deraadt@.

From dhartmei@ e-mail, ok henning@

of the n'th (n>1) file fails, the previous ones get removed before exit(1)
Idea by jason; ok millert deraadt

discussed and agreed theo and daniel

too small

dhclient needs this to validate old (but valid) leases in
/var/db/dhclient.leases in case it needs to fall back to such a
lease.  (the dhcp server can be down or not responding)
Reported by Chris Jepeway.
"makes sense"  henning dhartmei

well as the few userland tools which were only used on these platforms.

There has not been enough activity and interest towards these platform
to keep them lying in the tree.

icmp protocol naming particularly with pfctl, since the manpage is
icmp6(4) (not ipv6-icmp(4)).
suggested by espie@, cleared with deraadt@, ok dhartmei@

ok deraadt@