mlxsw: spectrum: Clear VLAN filters during port initialization

When a port is created, its VLAN filters are not cleared by the
firmware. This causes tagged packets to be later dropped by the ingress
STP filters, which default to DISCARD state.

The above did not matter much until commit b5ce611f ("mlxsw:
spectrum: Add devlink-trap support") where we exposed the drop reason to
users.

Without this patch, the drop reason users will see is not consistent. If
a port is enslaved to a VLAN-aware bridge and a packet with an invalid
VLAN tries to ingress the bridge, it will be dropped due to ingress STP
filter. If the VLAN is later enabled and then disabled, the packet will
be dropped by the ingress VLAN filter despite the above being a
seemingly NOP operation.

Fix this by clearing all the VLAN filters during port initialization.
Adjust the test accordingly.

Fixes: b5ce611f ("mlxsw: spectrum: Add devlink-trap support")
Reported-by: Alex Kushnarov <alexanderk@mellanox.com>
Tested-by: Alex Kushnarov <alexanderk@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>