[if_iwm] Partly sync if_iwm_binding.c to Linux iwlwifi code.
- Store macid and color values in struct iwm_vap, to avoid hardcoded constants a bit.
- Add iwm_mvm_binding_remove_vif() function (will be used in disconnecting from an access point without resetting the whole device).
- Not adding code from Linux iwlwifi yet, to handle one PHY context to be bound to several VAPs/virtual-interfaces, it's definitely not needed in the near future.
Obtained from: dragonflybsd.git f16ef74977e51e1bfc7a625dd18b98b02158e0e5