buildroot

lighttpd: source default file from startup script

lighttpd server runs cgi application that has no way to get environment
variables that are set up for it.

S50lighttpd is changed to source /etc/default/lighttpd file where these
environment variables can be set up.

Signed-off-by: Philipp Skadorov <philipp.skadorov@savoirfairelinux.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>