uapi linux/dlm_netlink.h: include linux/dlmconstants.h

Fixes userspace compilation error:

error: ‘DLM_RESNAME_MAXLEN’ undeclared here (not in a function)
  char resource_name[DLM_RESNAME_MAXLEN];
Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>
Signed-off-by: David Teigland <teigland@redhat.com>

include/uapi/linux/dlm_netlink.h

@@ -10,6 +10,7 @@
 #define _DLM_NETLINK_H
 
 #include <linux/types.h>
+#include <linux/dlmconstants.h>
 
 enum {
 	DLM_STATUS_WAITING = 1,