ng_netif: add ng_pktbuf and ng_netapi as dependencies

Though they are not needed in the code of `ng_netif` both `ng_pktbuf`
and `ng_netapi` are needed to use `ng_netif` in a sensible way.

Makefile.dep

@@ -52,6 +52,12 @@ ifneq (,$(filter ng_ipv6_nc,$(USEMODULE)))
     USEMODULE += ng_ipv6_addr
 endif
 
+ifneq (,$(filter ng_netif,$(USEMODULE)))
+    USEMODULE += ng_netapi
+    USEMODULE += ng_netreg
+    USEMODULE += ng_pktbuf
+endif
+
 ifneq (,$(filter aodvv2,$(USEMODULE)))
         USEMODULE += vtimer
         USEMODULE += sixlowpan