mlxsw: Set port STP state on bridge enslavement

mlxsw: Set port STP state on bridge enslavement

When the first port joins a LAG that already has a bridge upper, an
instance of struct mlxsw_sp_bridge_port is created for the LAG to keep
track of it as a bridge port. The bridge_port's STP state is initialized to
BR_STATE_DISABLED. This made sense previously, because mlxsw would only
ever allow a port to join a LAG if the LAG had no uppers. Thus if a
bridge_port was instantiated, it must have been because the LAG as such is
joining a bridge, and the STP state is correspondingly disabled.

However as of commit 2c5ffe8d7226 ("mlxsw: spectrum: Permit enslavement to
netdevices with uppers"), mlxsw allows a port to join a LAG that is already
a member of a bridge. The STP state may be different than disabled in that
case. Initialize it properly by querying the actual state.

This bug may cause an issue as traffic on ports attached to a bridged LAG
gets dropped on ingress with discard_ingress_general counter bumped.

Fixes: c6514f3627a0 ("Merge branch 'mlxsw-enslavement'")
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/39f4a5781050866b4132f350d7d8cf7ab23ea070.1691498735.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>