[test] Add okx() macro taking an explicit file name and line number

Allow test reports to specify an explicit file name and line number
using the extended okx() macro.  This allows large blocks of test
report code such as tcpip_random_ok() to be implemented as functions
rather than macros.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/test.h

  * Report test result
  *
  * @v success		Test succeeded
+ * @v file		File name
+ * @v line		Line number
  */
-#define ok( success ) do {					\
-	test_ok ( (success), __FILE__, __LINE__, #success );	\
-	} while ( 0 )
+#define okx( success, file, line ) \
+	test_ok ( success, file, line, #success )
+#define ok( success ) \
+	okx ( success, __FILE__, __LINE__ )
 
 #endif /* _IPXE_TEST_H */