send arp like packets for hvm live migration

send arp like packets for hvm live migration

When two servers connect different switch/hub and do live migration
between them, network connect will no reponse about 30 seconds,
it caused by migration finished, target server do not broadcast
guest os's network info.

In pvm, when backend changed, netfront driver will send fake arp
to network, so, hvm also need this.

Uri Lublin [wrote] the patch for it:
http://www.mail-archive.com/qemu-devel@nongnu.org/msg09306.html

I [Joe] add send arp like packets at tap_receive(), and it looked like
work fine.

Signed-off-by: Joe Jin <joe.jin@oracle.com>
Tested-by: Deepak Patel <deepak.patel@oracle.com>
CC: Keir Fraser <keir.fraser@eu.citrix.com>
CC: Kurt C. Hackel <kurt.hackel@oracle.com>
(cherry picked from commit 73b0037b2278812fcadadec9d8eac656f1716074)
Conflicts:
	vl.c