Let listen() return EDESTADDRREQ when not bound.

[ed]

Summary

We currently return EINVAL when calling listen() on a UNIX socket that has not been bound to a pathname. If my interpretation of POSIX is correct, we should return EDESTADDRREQ: "The socket is not bound to a local address, and the protocol does not support listening on an unbound socket."

Return EDESTADDRREQ instead when not bound and not connected.

Test Plan

This was spotted by the CloudABI test suite:

https://github.com/NuxiNL/cloudlibc/blob/master/src/libc/sys/socket/listen_test.c#L32

[gnn]

I don't know about POSIX but I do think that this is a good idea and a better error to return in this case.

[ed]

In D3038#59923, @gnn wrote:

I don't know about POSIX but I do think that this is a good idea and a better error to return in this case.

Perfect! Thanks for the quick review! I'll leave this code review open for another day. Will push it in if no one else objects.