Merge branch 'bridge-redirect-to-backup-port-when-port-is-administratively-down'

Ido Schimmel says:

====================
bridge: Redirect to backup port when port is administratively down

Patch #1 amends the bridge to redirect to the backup port when the
primary port is administratively down and not only when it does not have
a carrier. See the commit message for more details.

Patch #2 extends the bridge backup port selftest to cover this case.
====================

Link: https://patch.msgid.link/20250812080213.325298-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>