- netdev_features_t is only available in 3.3 and later kernels. Fix
vr_compat.h to account for this.

- num_possible_cpus() can return more CPUs than are present. Use
num_present_cpus() instead.
Merge pull request #61 from srajag/master

- netdev_features_t is only available in 3.3 and later kernels. Fix