Improve performance of RestrictAbusePorts

Switch the implementation of RestrictAbusePorts from a std::set to a
base::flat_set to reduce memory usage and improve data locality.

Use the base::flat_set::contains() method for lookup.

Skip invalid port numbers instead of crashing to reduce the damage of a
bad config push.

BUG=b:409713509
R=bashi@chromium.org

Change-Id: Ieed1851b61caa2a678b92fa3146351dc6193c454
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6486508
Auto-Submit: Adam Rice <ricea@chromium.org>
Reviewed-by: Tom Van Goethem <tov@chromium.org>
Commit-Queue: Tom Van Goethem <tov@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1450987}