Revert "unix: new implementation of unix/stream & unix/seqpacket"
The regressions in aio(4) and kernel RPC aren't a 5 minute problem.
This reverts commit d80a97def9a1db6f07f5d2e68f7ad62b27918947.
This reverts commit d1cbb17a873c787a527316bbb27551e97d5ad30c.
This reverts commit fb8a8333b481cc4256d0b3f0b5b4feaa4594e01f.