Error messaging in ipfw(8) was out of hand, almost 50 lines of usage

Error messaging in ipfw(8) was out of hand, almost 50 lines of usage
information for any command line error, the actual error message
almost always (and sometimes irretrievably) lost scrolling off the top
of the screen. Now just print the error. Give ipfw(8) no arguments for
the old usage summary.

Thanks to Lyndon Nerenberg <lyndon@orthanc.ab.ca> for the patch and
PR, but I had already done this when ru pointed out the PR.

PR:		bin/28729
Approved by:	ru
MFC after:	1 week