Runtime dir changed from /run to /run/pppd in commit 66a8c74c3f73 ("Let
./configure control the paths for pppd") and is likely to not exist on
some distros, in which case the pppdb will not be created.
See: #419 (lock directory moved in ppp-2.5.0) Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>