[SPR] Networking performance fix for concurrency with the dst_entry data structure

[Thibf]

This is a public version of https://bugs.launchpad.net/bugs/2028897

Backport:
bc9d3a9f2afc (net: dst: Switch to rcuref_t reference counting, 2023-03-23)
d288a162dd1c (net: dst: Prevent false sharing vs. dst_entry:: __refcnt, 2023-03-23)
e5ab9eff46b0 (atomics: Provide atomic_add_negative() variants, 2023-03-23)
ee1ee6db0779 (atomics: Provide rcuref - scalable reference counting, 2023-03-23)

merged in 6.4 to jammy.

[Impact]
  Address a bottleneck in the networking code related to struct dst_entry reference count, which results in networking performance loss with large number of connections, by adding rcuref as a scalable alternative solution.

  Developers report in the patch: The overall gain of both changes for localhost memtier ranges from 1.2X to 3.2X and from +2% to %5% range for networked operations on a 1Gb connection. A micro benchmark which enforces maximized concurrency shows a gain between 1.2X and 4.7X.

[Fix]

Upstream patch:
  bc9d3a9f2afc (net: dst: Switch to rcuref_t reference counting, 2023-03-23)
  d288a162dd1c (net: dst: Prevent false sharing vs. dst_entry:: __refcnt, 2023-03-23)
  e5ab9eff46b0 (atomics: Provide atomic_add_negative() variants, 2023-03-23)
  ee1ee6db0779 (atomics: Provide rcuref - scalable reference counting, 2023-03-23)

[Test Plan]

I have tested this code.

[Where problems could occur]

TODO