MFC: r333879, r342749

- Even though 64-bit atomics are supported on i386 there are panics
indicating that the code does not work correctly there. Switch
to mutex based variant (and fix that while we're here).
Reported by: pho, kib

- mp_ring: avoid items offset difference between iflib and mp_ring
on architectures without 64-bit atomics
Reported by: Augustin Cavalier <waddlesplash@gmail.com>

Merge iflib changes to 11-STABLE

MFC r300147, r300153, r300154, r300215, r301563, r301567,
r302372, r307560, r307562, r307563, r307568, r308792, r311039,
r311837, r312755, r312903, r312905, r312924, r313248, r315217,
r315245, r315288, r316278, r316281, r316502, r316596, r317756,
r319917, r319921, r319984, r319989, r320059, r320609, r320611,
r321253, r321629, r321630, r322337, r322338, r322823, r323077,
r323825, r323876, r323879, r323887, r323941, r323942, r323943,
r323944, r323954, r324038, r324318, r324937, r325166, r325167,
r325168, r325201, r325241, r325245, r325487, r325494, r325901,
r326033, r326369, r326370, r326432, r326577, r326578, r326702,
r326706, r326775, r327013, r327017, r327052, r327072, r327098,
r327242, r327244, r327247, r329651, r329742, r330289, r330715,
r330721, r332419, r332422, r332729

Reviewed by: sbruno
Approved by: re (delphij@)
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D15142

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

sys/net: more spelling.

Activate the NO_64BIT_ATOMICS code for mips and powerpc

Import the 'iflib' API library for network drivers. From the author:

"iflib is a library to eliminate the need for frequently duplicated device
independent logic propagated (poorly) across many network drivers."

Participation is purely optional. The IFLIB kernel config option is
provided for drivers that want to transition between legacy and iflib
modes of operation. ixl and ixgbe driver conversions will be committed
shortly. We hope to see participation from the Broadcom and maybe
Chelsio drivers in the near future.

Submitted by: mmacy@nextbsd.org
Reviewed by: gallatin
Differential Revision: D5211