IFAIU from the Bz, it works better (it does not timeout) if we use the more recent ipxe payload. I'm verifying this bug our images in 7.3 include: ipxe-roms-qemu-20150821-1.git4e03af8e.el7.noarch
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHBA-2016-0264.html