ulogd: provide default configure implementation

ulogd: provide default configure implementation

Provide a default implementation for the configure hook which simply
calls ulogd_parse_configfile(), so simple plugins only need to provide
the config_keyset. This also triggers an "unknown key" error if a
plugin defines no config_keyset (aka it has no options), but the config
file contains directives for it.

Signed-off-by: Corubba Smith <corubba@gmx.de>
Signed-off-by: Florian Westphal <fw@strlen.de>