These two patches enable making a live change to the nwfilter of a
guest's interface via virDomainUpdateDeviceFlags (virsh
update-device).
Differences from V1:
1) add patch from Stefan Berger to do a proper comparison of the
values stored in the filterparams hashtable.
2) simplify virNWFilterHashTableEqual to use Stefan's new function, and
remove a couple of pointless comparisons based on Stefan's review.