In pppd.mk the radattr.so plugin (for radiua) is installed twice (the second
install overwriting the first) but the radrealms.so plugin is omitted from
the install. This appears to be a copy-paste error.

Below is patch that corrects this.

signed-off by: Darcy Watkins <dwatkins@tranzeo.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>