net80211: LinuxKPI 802.11: clean up MIC vs. MMIC rx flags

net80211 used MMIC flags for CCMP instead of only for TKIP.
LinuxKPI 802.11 compat code (and later net80211) had a comment about
this. Given LinuxKPI seems to be the only consumer for these flags
currently outside of net80211 itself, clean them up before implementing
TKIP in LinuxKPI after all and before GCMP comes into the tree.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D49219