net/mlx5e: Fix deadlock in tc route query code

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Fix deadlock in tc route query code

Cited commit causes ABBA deadlock[0] when peer flows are created while
holding the devcom rw semaphore. Due to peer flows offload implementation
the lock is taken much higher up the call chain and there is no obvious way
to easily fix the deadlock. Instead, since tc route query code needs the
peer eswitch structure only to perform a lookup in xarray and doesn't
perform any sleeping operations with it, refactor the code for lockless
execution in following ways:

• RCUify the devcom 'data' pointer. When resetting the pointer
  synchronously wait for RCU grace period before returning. This is fine
  since devcom is currently only used for synchronization of
  pairing/unpairing of eswitches which is rare and already expensive as-is.

• Wrap all usages of 'paired' boolean in {READ|WRITE}_ONCE(). The flag has
  already been used in some unlocked contexts without proper
  annotations (e.g. users of mlx5_devcom_is_paired() function), but it wasn't
  an issue since all relevant code paths checked it again after obtaining the
  devcom semaphore. Now it is also used by mlx5_devcom_get_peer_data_rcu() as
  "best effort" check to return NULL when devcom is being unpaired. Note that
  while RCU read lock doesn't prevent the unpaired flag from being changed
  concurrently it still guarantees that reader can continue to use 'data'.

• Refactor mlx5e_tc_query_route_vport() function to use new
  mlx5…