iptables-restore: fix segmentation fault with -tanything

iptables-restore: fix segmentation fault with -tanything

Reference: Debian bug #458042

iptables-restore must not pass a table into do_command. It checks for
"-t arg" and "--table arg", but not "-targ". (On a related note,
using -targ does not work as expected).

This should fail gracefully, but crashes:

	iptables-restore <(echo -e '*filter\n-A INPUT -tx\nCOMMIT')

And this should use table "filter", or perhaps raise an error, but
instead sets the table to (literally) "-tfilter":

	iptables -tfilter -A INPUT

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>