[MFI] Supports BLE connection intervals down to 3.75ms (zephyrproject-rtos#22)

Modified BLE stack to allow for 3.75ms connection intervals which is needed by MFI when using g722 64kbps, 60 byte packet lengths

Author: kevin-whisper

subsys/bluetooth/host/hci_core.c

@@ -1485,9 +1485,9 @@ bool bt_le_conn_params_valid(const struct bt_le_conn_param *param)
 	/* All limits according to BT Core spec 5.0 [Vol 2, Part E, 7.8.12] */
 
 	// *** Whisper changed for MFI.  Previous minimum interval was 6 (7.5ms) but
-	// this needed to be modified to allow for intervals of 4 (5ms) for MFI streaming
+	// this needed to be modified to allow for intervals of 3 (3.75ms) for MFI streaming
 	if (param->interval_min > param->interval_max ||
-	    param->interval_min < 4 || param->interval_max > 3200) {
+	    param->interval_min < 3 || param->interval_max > 3200) {
 		return false;
 	}