Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Backport just the sys/{dev,modules}/cxgb{,e}/ parts of r237263, and then
disable the TOE and iWARP modules in the Makefiles (they won't compile
without the rest of r237263).

This reduces diffs between the cxgb/cxgbe drivers in head and 9 and
makes it easy to MFC other fixes to 9.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

- bump __FreeBSD version to reflect added buf_ring, memory barriers,
and ifnet functions

- add memory barriers to <machine/atomic.h>
- update drivers to only conditionally define their own

- add lockless producer / consumer ring buffer
- remove ring buffer implementation from cxgb and update its callers

- add if_transmit(struct ifnet *ifp, struct mbuf *m) to ifnet to
allow drivers to efficiently manage multiple hardware queues
(i.e. not serialize all packets through one ifq)
- expose if_qflush to allow drivers to flush any driver managed queues

This work was supported by Bitgravity Inc. and Chelsio Inc.

Update cxgb include paths to not require prefixing with dev/cxgb

Submitted by: Chelsio Inc.

import support for iwarp on Chelsio T3 card

Supported by Chelsio Inc.