wil6210: Drop plaintext frames on secure network

BugLink: https://bugs.launchpad.net/bugs/1931727



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>
(cherry picked from commit 236d53ab0b4aa37353f46e65dbd5806522d321ab)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>