vmxnet3: Pad short frames to minimum size (60 bytes)

vmxnet3: Pad short frames to minimum size (60 bytes)

When running VMware ESXi under qemu-kvm the guest discards frames
that are too short. Short ARP Requests will be dropped, this prevents
guests on the same bridge as VMware ESXi from communicating. This patch
simply adds the padding on the network device itself.

Signed-off-by: Ben Draper <ben@xrsa.net>
Reviewed-by: Dmitry Fleytman <dmitry@daynix.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(cherry picked from commit 40a87c6c9b11ef9c14e0301f76abf0eb2582f08e)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>