ath11k: Clear the fragment cache during key install

Currently the fragment cache setup during peer assoc is
cleared only during peer delete. In case a key reinstallation
happens with the same peer, the same fragment cache with old
fragments added before key installation could be clubbed
with fragments received after. This might be exploited
to mix fragments of different data resulting in a proper
unintended reassembled packet to be passed up the stack.

Hence flush the fragment cache on every key installation to prevent
potential attacks (CVE-2020-24587).

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.4.0.1-01734-QCAHKSWPL_SILICONZ-1 v2

Cc: stable@vger.kernel.org
Signed-off-by: Sriram R <srirrama@codeaurora.org>
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Link: https://lore.kernel.org/r/20210511200110.218dc777836f.I9af6fc76215a35936c4152552018afb5079c5d8c@changeid


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