ISDN: Fix act2000 compile error

Don't know when that broke, but somebody seems to be using "msg" in another
context - since we don't need the union to be named at all, it's easy to
fix.

drivers/isdn/act2000/capi.h

@@ -138,7 +138,7 @@ typedef struct actcapi_ncpd {
 
 typedef struct actcapi_msg {
 	actcapi_msghdr hdr;
-	union msg {
+	union {
 		__u16 manuf_msg;
 		struct manufacturer_req_net {
 			__u16 manuf_msg;