mlxsw: spectrum_acl: Set master RP index on transition to eRP

Bloom filter is updated on transitions from a single rule pattern,
also called master RP, to eRP table and vice versa. Since rules are
being written to or deleted from the Bloom filter on such transitions,
it is not required to keep the same eRP bank ID for the master RP.

Change master RP index assignment so it will be assigned with zero.
This is consistent with the assignment of the first available spot
that is used for allocating eRP's indices.

Signed-off-by: Nir Dotan <nird@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>