net-firewall/shorewall: Bumped to v4.6.x

Beginning with Shorewall 4.6 we moved from 6 packages,

  - shorewall-core
  - shorewall
  - shorewall6
  - shorewall-lite
  - shorewall6-lite
  - shorewall-init

to just one single "net-firewall/shorewall" package. Please see the new USE flags to control
which functionality you want to be installed.

We did this because the packages are proxy-maintained. Bumping 6 package for any required change
was too much work.