iptables: fix longopt reecognition and workaround getopt(3) behavior

* On the first call to getopt, opts was NULL, so long options would
not be recognized until a match/target was loaded.

Whacky getopt behavior:

* If the longopts parameter is NULL, getopt fails to recognize unknown
options, such that `iptables-multi main --append` will print a garbage
help message ("main needs an argument").

* If the longopts parameter is NULL on the first call, but not on
subsequent calls, it completely screws up option parsing, taking
the --dport in `iptables-multi main -A INPUT -p tcp --dport 1000`
as --destination instead, but not accepting "--destination 1.2.3.4"
either.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/ip6tables.c b/ip6tables.c
index 150893d..8318f91 100644
--- a/ip6tables.c
+++ b/ip6tables.c
@@ -147,6 +147,7 @@
 struct xtables_globals ip6tables_globals = {
 	.option_offset = 0,
 	.program_version = IPTABLES_VERSION,
+	.opts = original_opts,
 	.orig_opts = original_opts,
 	.exit_err = ip6tables_exit_error,
 };