backend/vxlan: Set the netmask of the IP used for the vxlan device
backend/vxlan: Set the netmask of the IP used for the vxlan device

Use a /32 netmask for the vxlan device. This avoids the kernel programming
broadcast routes (which won't work).

Unicast routes are already explicitly programmed so there's no need to
use a broader netmask.

coreos/flannel,coreos/flannel,coreos/flannel