Expand %%PREFIX%% in the rc script.
Create the group 'xorp' when the package is installed.
Fix the snmpd configure check and MIB module installation.
Fix the pkg-plist.
Note that as the XORP automake install target does not adhere to
hier(7), it may be desirable to specify PREFIX when building and/or
installing the port.
PR: ports/103879
Submitted by: Benjamin Black <ben@layer8.net>