Merge branch 'selftests-mlxsw-add-few-fixes-for-sharedbuffer-test'

Petr Machata says:

====================
selftests: mlxsw: Add few fixes for sharedbuffer test

Danielle Ratson writes:

Currently, the sharedbuffer test fails sometimes because it is reading a
maximum occupancy that is larger than expected on some different cases.

This is happening because the test assumes that the packet it is sending
is the only packet being passed to the device.

In addition, some duplications on one hand, and redundant test cases on
the other hand, were found in the test.

Add egress filters on h1 and h2 that will guarantee that the packets in
the buffer are sent in the test, and remove the redundant test cases.
====================

Link: https://patch.msgid.link/cover.1733414773.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>