net80211: crypto: ccmp: simplify and style(9)

Comply with style(9) and andd checks for booleaness when doing
bit tests.
If there is no need for double negated checks simplify them.
This all makes the conditions a lot easier to read.

Slip in a comment about MIC vs. MMIC.

No functional changes.

Sponsored by: The FreeBSD Foundation
Reviewed by: emaste, adrian
Differential Revision: https://reviews.freebsd.org/D49055

(cherry picked from commit 8dcdffdb086103e9ce36bfa82fc1179c88ebc31b)