docs(cadef): group CA operations together

modules/ca/src/client/cadef.h

@@ -141,6 +141,11 @@ typedef unsigned CA_SYNC_GID;
  *  External OP codes for CA operations
  */
 
+/**
+ * \name Channel Access operations
+ * @{
+ */
+
 /** \brief GET Channel Access operation. */
 #define CA_OP_GET             0
 /** \brief PUT Channel Access operation. */
@@ -172,6 +177,8 @@ typedef unsigned CA_SYNC_GID;
  */
 #define CA_OP_SEARCH        2
 
+/** @} */
+
 /** \brief Provides efficient test and display of channel access errors.
  *
  * SEVCHK() is a macro envelope around ca_signal() which only calls