mwifiex: drop gratuitous ARP frames

This patch adds support for dropping gratuitous ARP frames which is
requirement for WFA Hotspot2.0.

Hotspot2.0 capability is enabled in driver if extended capabilities
IE from BSS descriptor has 11u interworking enabled.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>