Fixes 40 ms wait time on consecutive network calls - linux only

Fixes #45 and #6287, at least on my machine.

```
julia> tic();for i=1:1000;fetch(remotecall(2,+,1,1));end;toc()
elapsed time: 0.490795733 seconds
0.490795733
julia> tic();for i=1:1000;remotecall_fetch(2,+,1,1);end;toc()
elapsed time: 0.209214712 seconds
0.209214712
```

I had to disable both Nagle and set QUICKACK.

@carlobaldassi, could you check with this patch?