wifi: wlcore: add pn16 support

wifi: wlcore: add pn16 support

TI Wl18xx firmware adds a "pn16" field for AES and TKIP keys as per
their patch:

https://git.ti.com/cgit/wilink8-wlan/build-utilites/tree/patches/kernel_patches/4.19.38/0023-wlcore-Fixing-PN-drift-on-encrypted-link-after-recov.patch?h=r8.9&id=a2ee50aa5190ed3b334373d6cd09b1bff56ffcf7

Add support for this, but rather than requiring the field to be
present (which would break existing firmwares), make it optional.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/E1sBsy7-00E8vu-Nc@rmk-PC.armlinux.org.uk