LibC: Add struct ifconf in net/if.h

This fixes building the scummvm port.

Userland/Libraries/LibC/net/if.h

@@ -46,6 +46,14 @@ struct ifreq {
 #define ifr_hwaddr ifr_ifru.ifru_hwaddr       // MAC address
 };
 
+struct ifconf {
+    int ifc_len;
+    union {
+        void* ifc_buf;
+        struct ifreq* ifc_req;
+    };
+};
+
 unsigned int if_nametoindex(const char* ifname);
 char* if_indextoname(unsigned int ifindex, char* ifname);