Fix the rc.d script-related problems with this port:
1. It's rc.d, not rcng
2. All new ports that use rc.d scripts need to use USE_RC_SUBR
3. The name of the script, PROVIDE, and $name should match the port name.
4. For the script itself:
a. Added a $FreeBSD$
b. Added KEYWORD: shutdown since it starts a persistent service.
c. Removed _flags from command=, it's spurious and will result in the
flags being included twice.
d. Moved the default variable assignment to after load_rc_config
e. Made the conf file a required_file, and added it to command_args
instead of _flags.
Approved by: maintainer