Merge branch 'net-dsa-yt921x-add-stp-mst-support'

David Yang says:

====================
net: dsa: yt921x: Add STP/MST support

Support for these features was deferred from the initial submission of the
driver.

v3: https://lore.kernel.org/20251126093240.2853294-1-mmyangfl@gmail.com
v2: https://lore.kernel.org/20251025170606.1937327-1-mmyangfl@gmail.com
v1: https://lore.kernel.org/20251024033237.1336249-1-mmyangfl@gmail.com
====================

Link: https://patch.msgid.link/20251201094232.3155105-1-mmyangfl@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>