sbin/ipfw: Allow tablearg as hostname

[donner]

Summary

Hostnames starting with "tablearg" are considered as a functional
argument instead of a literal.

Reported by: ae

Test Plan

The binary was supplied with some printf before and after the
transformation:

$ ipfw add fwd 0.0.0.0 from any to 'table(1)'
>>> 0.0.0.0 <<<
>>> 0.0.0.0 <<<

$ ipfw add fwd tablearg from any to 'table(1)'
>>> tablearg <<<
>>> 0.0.0.0 <<<

$ ipfw add fwd table,80 from any to 'table(1)'
>>> table,80 <<<
>>> table,80 <<<

$ ipfw add fwd tablearg,80 from any to 'table(1)'
>>> tablearg,80 <<<
>>> 0.0.0.0,80 <<<

$ ipfw add fwd tableargs.test from any to 'table(1)'
>>> tableargs.test <<<
>>> tableargs.test <<<

$ ipfw add fwd tablearg.local:80 from any to 'table(1)'
>>> tablearg.local:80 <<<
>>> tablearg.local:80 <<<