ctladm: don't require the use of "-p" with "port -r"

When removing a port, the ioctl frontend requires the "-p" argument.
But other frontends, like cfiscsi, do not. So don't require that
argument in the ctladm command. The frontend driver will report an
error if any required argument is missing.

Sponsored by: Axcient
Reviewed by: mav
Pull Request: https://github.com/freebsd/freebsd-src/pull/1279

(cherry picked from commit edbd489d09babebdc6c03924a912013be584c409)

ctladm: don't require the use of "-p" with "port -r", part 2

• Remove a now superfluous FALLTHROUGH hint
• Don't specify "-p" with an empty argument in the tests

Reported by: jhb

(cherry picked from commit 7f50027321db3b08477f6236abded0297e9e5ed8)