Regression - bridged networking broken for Mac OS X guest

Using the instructions at http://www.contrib.andrew.cmu.edu/~somlo/OSXKVM/ for running Mac OS X Snow Leopard under QEMU, bridged networking is broken when using QEMU git. The result is that Mac OS X is unable to obtain an IP address using DHCP. It works in the latest stable release - QEMU 2.3.0.

Replace "-netdev user,id=hub0port0" with "-netdev bridge,br=br0,id=hub0port0" when testing bridged networking.

Bisecting the git repository shows the following bad commit:
commit a90a7425cf592a3afeff3eaf32f543b83050ee5c
Author: Fam Zheng <email address hidden>
Date:   Thu Jun 4 14:45:17 2015 +0800

    tap: Drop tap_can_send

    This callback is called by main loop before polling s->fd, if it returns
    false, the fd will not be polled in this iteration.

    This is redundant with checks inside read callback. After this patch,
    the data will be sent to peer when it arrives. If the device can't
    receive, it will be queued to incoming_queue, and when the device status
    changes, this queue will be flushed.

    Signed-off-by: Fam Zheng <email address hidden>
    Message-id: <email address hidden>
    Signed-off-by: Stefan Hajnoczi <email address hidden>