viced: Force valid host enumeration flags

viced: Force valid host enumeration flags

Make sure that the callback functions for h_Enumerate and
h_Enumerate_r give us back valid flags values by aborting if they
return an invalid value.

Change-Id: Id34b461d5452ac318a1714b6c3ffdaf41015995c
Reviewed-on: http://gerrit.openafs.org/4528
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>