wl12xx: consider encryption and QoS in auto arp template

When configuring the arp response template,
and encryption is enabled, we should add some
space and set the protected flag bit in the fc.

In order to track the encryption type, set
wlvif->encryption_type when setting an encryption key,
and reconfigure the arp response. Clear this field on
wl1271_join, as keys have to be re-configured
anyway after a join command.

Similarly, track whether QoS is configured.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>