Rename get_first_advertised_{addr,port}_by_type_af().

Rationale: these don't actually give the first advertised
address/port, but instead give us the first such port that we are
_configured_ to advertise.  Putting them in a portconf_ namespace
therefore makes sense.

Similarly, there are no other functions that get the first
configured advertised addr/port, so the "by_type_af()" part is needless.

This is an automated commit, generated by this command:

./scripts/maint/rename_c_identifier.py \
        get_first_advertised_addr_by_type_af portconf_get_first_advertised_addr \
        get_first_advertised_port_by_type_af portconf_get_first_advertised_port