xtables-monitor: Print commands instead of -4/-6/-0 flags

xtables-monitor: Print commands instead of -4/-6/-0 flags

The '-4' and '-6' flags are a rarely used feature of iptables-restore.
The '-0' flag is purely artificial and not recognized anywhere (at least
not as an arptables rule prefix in this sense). Finally, there is no
such flag for ebtables in the first place. Go with a more intuitively
clear approach and instead print the typical command which added the
rule being printed.

Signed-off-by: Phil Sutter <phil@nwl.cc>