conf: add missing virxml.h include for nwfilter_params.h

The nwfilter_params.h header references the xmlNodePtr type, so must
include the virxml.h header to get the libxml2 types defined.
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

src/conf/nwfilter_params.h

@@ -26,6 +26,7 @@
 # include "virhash.h"
 # include "virbuffer.h"
 # include "virmacaddr.h"
+# include "virxml.h"
 
 typedef enum {
     NWFILTER_VALUE_TYPE_SIMPLE,