Added ENABLE_UPNPPINHOLE, and using that to compile in the support for pinholes. It is enabled by either ENABLE_6CF_SERVICE or ENABLE_PCP + ENABLE_IPV6.
Some initial effort at actually adding pinhole support to PCP code.
Fixed PEER supporting PCP to compile too.
Added Linux get_pinhole_uid_by_index.
INET_ADDRSTRLEN => PCP_ADDRSTRLEN, some minor fixing.
Compilation fixes on Linux + tentative pf desc NOP changes as well.