mlxsw: spectrum_router: Increase parsing depth for multipath hash

Commit 01848e05 ("mlxsw: spectrum_router: Add support for inner
layer 3 multipath hash policy") and commit daeabf89 ("mlxsw:
spectrum_router: Add support for custom multipath hash policy") added
support for multipath hash policies where the hash is calculated based
on inner packet fields.

For IPv6-in-IPv6 packets, the default parsing depth (96 bytes) is not
enough when these policies are used.

Therefore, for such cases, call the new API to increase / decrease the
parsing depth as necessary. Care is taken to ensure the API is not
called multiple times.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>