[infiniband] Add find_ibdev()

src/include/gpxe/infiniband.h

 extern struct ib_device * alloc_ibdev ( size_t priv_size );
 extern int register_ibdev ( struct ib_device *ibdev );
 extern void unregister_ibdev ( struct ib_device *ibdev );
+extern struct ib_device * find_ibdev ( struct ib_gid *gid );
 extern void ib_link_state_changed ( struct ib_device *ibdev );
 extern void ib_poll_eq ( struct ib_device *ibdev );
 extern struct list_head ib_devices;

src/net/infiniband.c

 	ibdev_put ( ibdev );
 	DBGC ( ibdev, "IBDEV %p unregistered\n", ibdev );
 }
+
+/**
+ * Find Infiniband device by GID
+ *
+ * @v gid		GID
+ * @ret ibdev		Infiniband device, or NULL
+ */
+struct ib_device * find_ibdev ( struct ib_gid *gid ) {
+	struct ib_device *ibdev;
+
+	for_each_ibdev ( ibdev ) {
+		if ( memcmp ( gid, &ibdev->gid, sizeof ( *gid ) ) == 0 )
+			return ibdev;
+	}
+	return NULL;
+}