The problem with socket aio(4) is that it uses socket buffer locks for
queueing and piggybacking on this locking calls soreadable() and
sowriteable() directly. Ideally it should use pr_sopoll() method.

At this point solve the problem on the side of unix(4), but ideally
it should be socket aio(4) problem (not a first class citizen) than
problem of unix(4), definitely a primary facility.

This shall be squashed into the main new unix(4) commit.