FROMGIT: rxrpc: Use call_rcu_flush() instead of call_rcu()

call_rcu() changes to save power may cause slowness. Use the
call_rcu_flush() API instead which reverts to the old behavior.

We find this via inspection that the RCU callback does a wakeup of a
thread. This usually indicates that something is waiting on it. To be
safe, let us use call_rcu_flush() here instead.

(cherry picked from commit f32846476afbe1f296c41d036219178b3dfb6a9d
 https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git

 rcu/next)

BUG=b:222463781
TEST=powerIdle lab tests.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.corp-partner.google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3965078


Reviewed-by: Ross Zwisler <zwisler@google.com>
Change-Id: Iaadfe2f9db189489915828c6f2f74522f4b90ea3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4069546