treewide: Use ell's useful.h header

src/ap.c

@@ -33,6 +33,7 @@
 
 #include "linux/nl80211.h"
 
+#include "ell/useful.h"
 #include "src/missing.h"
 #include "src/iwd.h"
 #include "src/module.h"

src/erp.c

@@ -30,6 +30,7 @@
 
 #include <ell/ell.h>
 
+#include "ell/useful.h"
 #include "src/missing.h"
 #include "src/iwd.h"
 #include "src/module.h"

src/frame-xchg.c

@@ -33,6 +33,7 @@
 
 #include "linux/nl80211.h"
 
+#include "ell/useful.h"
 #include "src/iwd.h"
 #include "src/module.h"
 #include "src/mpdu.h"

src/knownnetworks.c

@@ -34,6 +34,7 @@
 
 #include <ell/ell.h>
 
+#include "ell/useful.h"
 #include "src/iwd.h"
 #include "src/module.h"
 #include "src/storage.h"

src/netconfig.c

@@ -39,6 +39,7 @@
 
 #include <ell/ell.h>
 
+#include "ell/useful.h"
 #include "src/iwd.h"
 #include "src/module.h"
 #include "src/netdev.h"

src/p2p.c

@@ -39,6 +39,7 @@
 
 #include "linux/nl80211.h"
 
+#include "ell/useful.h"
 #include "src/missing.h"
 #include "src/iwd.h"
 #include "src/wiphy.h"

src/scan.c

@@ -35,6 +35,7 @@
 #include <linux/if_ether.h>
 #include <ell/ell.h>
 
+#include "ell/useful.h"
 #include "linux/nl80211.h"
 #include "src/iwd.h"
 #include "src/module.h"