libxt_HMARK: correct a number of errors introduced by Pablo's rework

* Fix typo in --hmark-rnd description.
* Remove trailing -set from port and spi options.
* Take missing value for ports and spi from command line.
* Fix spi / port validation.
* Remove --hmark-offset as mandatory.

Signed-off-by: Hans Schillstrom <hans@schillstrom.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
1 file changed