Add network address and socket types

Types and methods for dealing with IPv4 and IPv6 addresses (and UNIX
domain socket addresses under UNIX). This does not include code for
actual socket I/O.

Originally from "gnio". Much of the code was written by Christian
Kellner, Samuel Cormier-Iijima, and Ryan Lortie.

Part of #548466.

gio/gioenums.h

@@ -477,6 +477,26 @@ typedef enum  {
 } GEmblemOrigin;
 
 
+/**
+ * GSocketFamily:
+ * @G_SOCKET_FAMILY_INVALID: no address family
+ * @G_SOCKET_FAMILY_IPV4: the IPv4 family
+ * @G_SOCKET_FAMILY_IPV6: the IPv6 family
+ * @G_SOCKET_FAMILY_UNIX: the UNIX domain family
+ *
+ * The protocol family of a #GSocketAddress. (These values are
+ * identical to the system defines %AF_INET, %AF_INET6 and %AF_UNIX,
+ * if available.)
+ */
+typedef enum {
+  G_SOCKET_FAMILY_INVALID,
+#ifdef GLIB_SYSDEF_AF_UNIX
+  G_SOCKET_FAMILY_UNIX = GLIB_SYSDEF_AF_UNIX,
+#endif
+  G_SOCKET_FAMILY_IPV4 = GLIB_SYSDEF_AF_INET,
+  G_SOCKET_FAMILY_IPV6 = GLIB_SYSDEF_AF_INET6
+} GSocketFamily;
+
 G_END_DECLS
 
 #endif /* __GIO_ENUMS_H__ */