(split) Return the correct status if ieee80211_ff_check() consumes the mbuf.

I broke this when converting the net80211 TX path to use if_transmit.
(split) Don't return ENOTSUPP here - the net80211 pluggable ioctl API will treat
this as the final item in the linker set and not try others.

This stopped the fast frames IOCTLs from being called.
(split) Add m_clrprotoflags() to clear protocol specific mbuf flags at up and
downwards layer crossings.

Consistently use it within IP, IPv6 and ethernet protocols.

Discussed with:	trociny, glebius
(split) Migrate the net80211 protocol specific use of M_FRAG, M_FIRSTFRAG and
M_LASTFRAG flags to protocol specific flags.

Remove the now unused M_FRAG, M_FIRSTFRAG and M_LASTFRAG mbuf flags.

Discussed with:	trociny, glebius, adrian
(split) Reorder the mbuf defines to make more sense and group related flags
together.

Add M_FLAG_PRINTF for use with printf(9) %b indentifier.

Use the generic mbuf flags print names in the net80211 code and adjust
the protocol specific bits for their new positions.

Change SCTP M_PROTO mapping from 5 to 1 to fit within the 16bit field
they use internally to store some additional information.

Discussed with:	trociny, glebius
(split) Merge commit '7bc0ae60'
(split) Merge commit '7fb3e64ee'
(split) Merge commit 'bea80a70'