wil6210: Drop plaintext frames on secure network

On secure network, only eap frames are valid unencrypted frames and
allowed to be indicated to the local network, any other unencrypted
frame should be dropped immediately.

Change-Id: Id9d97a4c0984f7bf2d7d6941c4c61e87bc2354cd
Signed-off-by: Ahmad Masri <amasri@codeaurora.org>