cfg80211: Check if PMKID attribute is of expected size

nla policy checks for only maximum length of the attribute data
when the attribute type is NLA_BINARY. If userspace sends less
data than specified, the wireless drivers may access illegal
memory. When type is NLA_UNSPEC, nla policy check ensures that
userspace sends minimum specified length number of bytes.

Remove type assignment to NLA_BINARY from nla_policy of
NL80211_ATTR_PMKID to make this NLA_UNSPEC and to make sure minimum
WLAN_PMKID_LEN bytes are received from userspace with
NL80211_ATTR_PMKID.

Fixes: 67fbb16b

 ("nl80211: PMKSA caching support")
Cc: stable@vger.kernel.org
Signed-off-by: Srinivas Dasari <dasaris@qti.qualcomm.com>
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>