ifconfig(8): Partial revert of r347241

r347241 introduced an ifname <-> kld mapping table, mostly so tun/tap/vmnet
can autoload the correct module on use. It also inadvertently made bogus
some previously valid uses of sizeof().

Revert back to ifkind on the stack for simplicity sake. This reduces the
diff from the previous version of ifmaybeload for easiser auditing.