optimize: add unsupported statement

optimize: add unsupported statement

Do not try to merge rules with unsupported statements. This patch adds a
dummy unsupported statement which is included in the statement
collection and the rule vs statement matrix.

When looking for possible rule mergers, rules using unsupported
statements are discarded, otherwise bogus rule mergers might occur.

Note that __stmt_type_eq() already returns false for unsupported
statements.

Add a test using meta mark statement, which is not yet supported.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>