Libertas: cfg80211 support

Libertas: cfg80211 support

Holger Schurig's patch (https://patchwork.kernel.org/patch/64286/)
is rebased to latest wireless-testing tree.

(Includes patches from me originally posted as "libertas: fix build
error due to undefined symbol" and "libertas: unmangle capability
value". -- JWL)

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kiran Divekar <dkiran@marvell.com>
Tested-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>