nl80211: rework internal_flags usage

Since internal_flags is only 8 bits, we can only have one
more internal flag. However, we can obviously never use all
of possible the combinations, in fact, we only use 14 of
them (including no flags).

Since we want more flags for MLO (multi-link operation) in
the future, refactor the code to use a flags selector, so
wrap all of the .internal_flags assignments in a IFLAGS()
macro which selects the combination according to the pre-
defined list of combinations.

When we need a new combination, we'll have to add it, but
again we will never use all possible combinations.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20220414140402.70ddf8af3eb0.I2cc38cb6a10bb4c3863ec9ee97edbcc70a07aa4b@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>