354019-354020,354037,354040,354042,354045-354046,354053,354081,
  354084:

2nd half of the major frag6 rework and adding test cases.

Cleanup structures, fix vnet teardown leak, add sysctls, whitespace
cahnges, replace KAME hand-rolled queues with queue(9) TAILQs,
comments, small improvements, do not leak packet queue entry in error
case, fix counter leak in error case and optimise code, handling of
overlapping fragments to conform to RFC 8200, prevent overwriting initial
fragoff=0 packet meta-data.

Submitted by:	jtl (initally, partially)
Sponsored by:	Netflix (initially)