Merge branch 'mlxsw-mphash-policies'

Ido Schimmel says:

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mlxsw: Add support for new multipath hash policies

This patchset adds support for two new multipath hash policies in mlxsw.

Patch #1 emits net events whenever the
net.ipv{4,6}.fib_multipath_hash_fields sysctls are changed. This allows
listeners to react to changes in the packet fields used for the
computation of the multipath hash.

Patches #2-#3 refactor the code in mlxsw that is responsible for the
configuration of the multipath hash, so that it will be easier to extend
for the two new policies.

Patch #4 adds the register fields required to support the new policies.

Patch #5-#7 add support for inner layer 3 and custom multipath hash
policies.

Tested using following forwarding selftests:

* custom_multipath_hash.sh
* gre_custom_multipath_hash.sh
* gre_inner_v4_multipath.sh
* gre_inner_v6_multipath.sh
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