MPD: FreeBSD PPP daemon

This patch adds two macros which enable the use of the local and remote IP
address of the link to be used in generating IPFW rules with the RADIUS
VSAs mpd-table, mpd-table-static, mpd-rule.

The patch replaces %a1 with the remote IP address, and %a2 with the local
IP address. Thus, we can tell MPD for example to put the remote IP address
in a table specified by the RADIUS VSA. Sample radius entry, which will put
the peer IP address in table 1(+the default offset defined):
mpd-table += 1=%a1

This is very useful for mass shaping different service types, etc.

The current function for parsing macros searches for a %+char+digit, so, in
order to not parse each line again, the %a1 and %a2 macros were chosen,
though not so descriptive.

Hope that gets included in the official MPD release, if you need any change
or suggest another macro names or sth else, please drop me a line at
root--at--net1--dot--cc