iptables: reset options at the start of each command

iptables: reset options at the start of each command

For each new command, iptables is supposed to start afresh with a
blank option set (opts) that only contains the program-specific
options (orig_opts), without any extension options. We failed to
restore this pointer (in function do_command) after the previous free
call in xtables_free_opts.

Reported-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>