Continuous integration caught that although 'make syntax-check' was
sufficient to let me be aware that I had to change bhyve to use
s/virDomainShutdownEnsureACL/virDomainShutdownFlagsEnsureACL/, it was
not sufficient to note which ACL functions require 2 vs. 3 arguments
for flag validation.

Fixes: eded8aadSigned-off-by: NEric Blake <eblake@redhat.com>