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
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D49219

(cherry picked from commit 394a9a5b1c2ad7b679a00c3087c41378abfa74a1)
(cherry picked from commit 5f2893553f3cde7c1529f9ca3987be378a9b7025)