UPSTREAM: nl80211: use RCU to read regdom in reg get/dump

Use RCU here to read the regdomain, this will allow us
to remove the RTNL locking from the setter.

Note in nl80211_get_reg_do() we still need the RTNL to
do the wiphy lookup.

Link: https://lore.kernel.org/r/20220214101820.5d4acbcf2a46.Ibfc91980439862125e983d9adeebaba73fe38e2d@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Bug: 238103864
Change-Id: I33a5e791848dff6794ff2c53661de0de50447a72
(cherry picked from commit 024fcf5e)
Signed-off-by: Veerendranath Jakkam <quic_vjakkam@quicinc.com>