pbrd, zebra: fix zapi and netlink rule encoding

pbrd, zebra: fix zapi and netlink rule encoding

In pbrd, don't encode a rule without a table. There are cases
where the zapi encoding was incorrect because the 4-octet
table id was missing. In zebra, mask off the ECN bits in the
TOS byte when encoding an iprule to match netlink's
expectation.

Signed-off-by: Mark Stapp <mjs@labn.net>
(cherry picked from commit 4112baec9f7ec235c66e2c5992ba2288ca1557e7)