Don't set SO_RCVBUF on UNIX sockets.

[eddyb]

Fixes servo/servo#10260, although this might not be even a reasonable approach.
At this point it's mostly guesswork and Servo needs a lot more testing on linux.

[Manishearth]

r? @pcwalton

[pcwalton]

Bluh?

I mean, r=me I guess, but this is kinda scary…

[samlh]

Pure speculation: if there are multiple senders, then perhaps the receive buffer needs to be large enough to receive from all simultaneously?

[antrik]

That's more than scary. For one, this will be very inefficient AIUI, as the receiver will always allocate a large receive buffer (208 KiB on x64 systems), but only ever use a small part of it...

More importantly, I don't see how this could really fix anything -- more likely it only papers over some other problem. In fact I believe I even know what exactly. I have some changes for that in the pipeline -- though they were meant only as (minor) optimisation and code simplification; I didn't realise until now that it's actually likely to cause bugs...

Investigating that will have to wait a day or two though.

[eddyb]

Closed in favor of #60.