There was a race condition in SMP that an ath10k_peer was created but its
member sta was null. Following are procedures of ath10k_peer creation and
member sta access in peer statistics path.
Any access of peer->sta after peer was added to peer_map but before sta was
assigned could cause a null pointer issue. And because these two steps are
asynchronous, no proper lock can protect them. So both peer and sta need to
be checked before access.
Tested: QCA9984 with firmware ver 10.4-3.9.0.1-00005 Signed-off-by: Zhi Chen <zhichen@codeaurora.org> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>