[docs] correcting Doxygen tags (#2510)

* [docs] correcting Doxygen tag

* [docs] fix misspelled Doxygen tag

* [docs] add Channel Monitoring to Doxygen hierarchy

include/openthread/link.h

@@ -154,7 +154,7 @@ OTAPI bool OTCALL otLinkIsInTransmitState(otInstance *aInstance);
  * This function enqueues an IEEE 802.15.4 out of band Frame for transmission.
  *
  * @param[in] aInstance  A pointer to an OpenThread instance.
- * @parma[in] aOobFrame  A pointer to the frame to transmit.
+ * @param[in] aOobFrame  A pointer to the frame to transmit.
  *
  * @retval OT_ERROR_NONE           Successfully enqueued an IEEE 802.15.4 Data Request message.
  * @retval OT_ERROR_ALREADY        An IEEE 802.15.4 out of band frame is already enqueued.

include/openthread/ncp.h

@@ -184,7 +184,7 @@ void otNcpHandleLegacyNodeDidJoin(const otExtAddress *aExtAddr);
  * This callback is invoked by the legacy stack to notify that the
  * legacy ULA prefix has changed.
  *
- * param[in]    aUlaPrefix  A pointer to the received ULA prefix.
+ * @param[in]    aUlaPrefix  A pointer to the received ULA prefix.
  *
  */
 void otNcpHandleDidReceiveNewLegacyUlaPrefix(const uint8_t *aUlaPrefix);

include/openthread/openthread.h

@@ -111,6 +111,7 @@ extern "C" {
  *
  * @{
  *
+ * @defgroup api-channel-monitor     Channel Monitoring
  * @defgroup api-child-supervision   Child Supervision
  * @defgroup api-coap                CoAP
  * @defgroup api-cli                 Command Line Interface