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