maint: add required includes

Some files do not include what they use and rely on virutil.h
to pull in the necessary header files.

Fix it.

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>

src/nwfilter/nwfilter_ebiptables_driver.c

@@ -22,6 +22,7 @@
 
 #include <config.h>
 
+#include <unistd.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <sys/utsname.h>

src/util/virfirewalld.c

@@ -32,6 +32,7 @@
 #include "virlog.h"
 #include "virgdbus.h"
 #include "virenum.h"
+#include "virstring.h"
 
 #define VIR_FROM_THIS VIR_FROM_FIREWALLD