mlxsw: spectrum_acl: Allow to interrupt/continue rehash work

Currently, migration of vregions with many entries may take long time
during which insertions and removals of the rules are blocked
due to wait to acquire vregion->lock.

To overcome this, allow to interrupt and continue rehash work according
to the set credits - number of rules to migrate.

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