Wifi: Add 6GHz band to NAN structures and methods

This commit adds 6GHz band to NAN related structures and methods.

Bug: 139354972
Test: Manual
Test: VTS test
Test: Unit test:
Test: ./hardware/interfaces/wifi/1.4/default/tests/runtests.sh
Change-Id: I33f63fde67d5a839678076fdb7c76d5eb8645131