Rework socket handling again. Rather than

Rework socket handling again.  Rather than
issuing ioctls to a random socket and just
hoping, we do our best to pick the right one
for the address family in use.  This should
fix a bug reported for 1.47 where a command like
"ifconfig eth0 broadcast 1.0.0.255" picked on the
AF_APPLETALK socket and so didn't work.

Quite an invasive fix but hopefully the right one.
Andi, can you take a look since this is stuff you've
been working on recently.