mlxsw: spectrum: Remove RIF from PVID vPort when joining / leaving LAG

We are going to assign router interfaces (RIFs) to netdevs if an IPv4
address was assigned to them. If one was assigned to a port netdev, this
will translate to the PVID vPort being member in a RIF.

While it's possible for a LAG slave to have an IP address, we can't have
a vPort being member in two FIDs (assuming the LAG device will be
put in bridge / assigned an IP address).

Solve that by making the PVID vPort leave any FID it might be a member
in when joining / leaving LAG.

Note that the PVID vPort is the only vPort that can be present on the
port when it's put under LAG.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>