nl80211: Add a handler to create_interface

nl80211: Add a handler to create_interface

Add an option to pass a handler to nl80211_create_iface() and
nl80211_create_interface_once() that will be called after receiving the
message from the kernel. This handler will add the option to process the
message in different ways for different interfaces.

Signed-off-by: David Spinadel <david.spinadel@intel.com>