rework try_then_request_module to do less in non-modular kernels

This reworks try_then_request_module to only invoke the "lookup"
function "x" once when the kernel is not modular.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

include/linux/kmod.h

@@ -29,11 +29,12 @@
 /* modprobe exit status on success, -ve on error.  Return value
  * usually useless though. */
 extern int request_module(const char * name, ...) __attribute__ ((format (printf, 1, 2)));
+#define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
 #else
 static inline int request_module(const char * name, ...) { return -ENOSYS; }
+#define try_then_request_module(x, mod...) (x)
 #endif
 
-#define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
 
 struct key;
 struct file;