inet: silence message about exceptions not being implemented for select(UDP)

This message generates a lot of noise with openntpd. Hide it unless DEBUG is
turned on.

servers/inet/generic/udp.c

@@ -316,10 +316,12 @@ unsigned operations;
 		/* Should handle special case when the interface is down */
 		resops |= SR_SELECT_WRITE;
 	}
+#if DEBUG == 1
 	if (operations & SR_SELECT_EXCEPTION)
 	{
 		printf("udp_select: not implemented for exceptions\n");
 	}
+#endif
 	return resops;
 }