mlxsw: spectrum_router: Update hardware flags on nexthop buckets

So far, mlxsw only updated hardware flags ('offload' / 'trap') on
nexthop objects. For resilient nexthop groups, these flags need to be
updated on individual nexthop buckets as well.

Update these flags whenever updating the flags of the encapsulating
nexthop object and whenever a nexthop bucket is replaced.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>