offset tuning -> bias tee hack

Use the offset tuning button to enable the bias tee on the V3. Offset tuning is not used for the R820T so this is okay and allows us to toggle the bias tee on software that hasn't implemented specific bias tee controls.

src/librtlsdr.c

@@ -1249,6 +1249,9 @@ int rtlsdr_set_offset_tuning(rtlsdr_dev_t *dev, int on)
 
 	if ((dev->tuner_type == RTLSDR_TUNER_R820T) ||
 	    (dev->tuner_type == RTLSDR_TUNER_R828D))
+		// RTL-SDR-BLOG Hack, enables us to turn on the bias tee by clicking on "offset tuning" in software that doesn't have specified bias tee support.
+		// Offset tuning is not used for R820T devices so it is no problem.
+		rtlsdr_set_gpio(dev, 0, on);
 		return -2;
 
 	if (dev->direct_sampling)