Include opt_ah.h when compiling the driver.

There are HAL methods which are actually direct register
access, rather than simply HAL calls. Because of this, these
register accesses would use the non-debug path in ah_osdep.h
as opt_ah.h isn't included.

With this, the correct register access methods are used,
so debugging traces show things such as TXDP checking and
TSF32 access.

sys/dev/ath/if_ath.c

@@ -39,6 +39,11 @@ __FBSDID("$FreeBSD$");
 
 #include "opt_inet.h"
 #include "opt_ath.h"
+/*
+ * This is needed for register operations which are performed
+ * by the driver - eg, calls to ath_hal_gettsf32().
+ */
+#include "opt_ah.h"
 #include "opt_wlan.h"
 
 #include <sys/param.h>