wlan: Change RSNOpaque Min len to 2

WPA2 Security Improvements test plan case 4.2.2
Scenario F: RSN version Field is truncated to 1
octet. That means the test bed will send assoc
request with RSN ie total size 3.
Current driver unpack_core will return
DOT11F_INCOMPLETE_IE and doesn't extract the
incomplete RSN ie data.
lim_check_wpa_rsn_ie will have no chance to
run dot11f_unpack_ie_rsn to reject the assoc
request frame because the assoc_req->rsnPresent
is 0.
Change RSN Opaque Min Len to 2 (data min len 0),
so that the unpack_core can extract the RSN ie
even though it is "INCOMPLETE", and then
the later lim_check_wpa_rsn_ie can reject such
assoc request.

Change-Id: Icba37840ea6eb1cc1c2c225efd9ec58757606eea
CRs-Fixed: 2336766