wireless: fix VHT max AMPDU exponent definition

This is really a 3-bit field, not a single bit,
so declare a mask and shift. Also fix hwsim, it
advertises the maximum possible.

While at it reindent all the defines using tabs
instead of spaces.

Change-Id: I7cd81c0d72f76deb5010aba5bfa3dd312006e898
Signed-off-by: Johannes Berg <johannes.berg@intel.com>