Port 2.7: logformat tag for logging the outgoing IP address (tcp_outgoing_address)

Port 2.7: logformat tag for logging the outgoing IP address (tcp_outgoing_address)

This adds the log format to log the local IP address used on outgoing
connections to peers and servers. Squid-2.7 called this %oa.

However it is a perfectly matching part of the existing set of %la and
%lp (local inbound) and %<lp (local outbound port).

As such, the %oa is accepted as input for backward compatibility, but the
Squid-3 version is: %<la

This is based only very loosely on the Squid-2 %oa work by Andrew Atangulov