Revert "Wait for packets to be accepted before returning from writev"

Linux dom0 and Xen have been patched to fix the underlying bug, and
this work-around made things really slow.

This reverts commit aa5061b8ffdc2e34968e80ed745ffd77372fa358.
Merge pull request #12 from talex5/master

Revert "Wait for packets to be accepted before returning from writev"