Raise the part of torrc mapaddress handling that knows wildcards

Raise the part of torrc mapaddress handling that knows wildcards

This patch extracts the inner part of config_register_addressmaps --
the part that knows about detecting wildcard addresses addresses --
and makes it into a new function.  The new function is deliberately
not moved or reindented, so that the diff is smaller.

I need this to fix bug 6244.