NSX: Optionally not enforce nat rule match length check

This patch adds the 'raise_on_len_mismatch' parameter to the
'delete_nat_rules_by_match' function. The plugin then leverages
this parameter for ensuring NAT rules deletion operations
are completed successfully even when duplicate rules are found
or no corresponding rules are found at all.

With this change, the 'remove_router_interface' operation will
correctly complete even in cases when NAT rules in Neutron and
the NSX backend are out of sync.

This patch also changes a check in delete_nat_rules_by_match in
order to make it less expensive.

Closes-Bug: 1328181

Change-Id: I856d67ef5ff6264374cb8f2569668da4c205ad9f
Merge "NSX: Optionally not enforce nat rule match length check"