The virfirewalld.h file provides a declaration for
virFirewallDApplyRule() which accepts an argument of type
virFirewallLayer. But the typedef lives in virfirewall.h and thus
including just virfirewalld.h is not sufficient.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> Reviewed-by: Kristina Hanicova <khanicov@redhat.com>