[3329] ioReady methods were missing commentary in dhcp_ddns.

Adding missing commentary in ncr_io.h and ncr_upd.h

src/lib/dhcp_ddns/ncr_io.h

@@ -576,6 +576,9 @@ public:
     /// @throw NcrSenderError if the sender is not in send mode,
     virtual int getSelectFd() = 0;
 
+    /// @brief Returns whether or not the sender has IO ready to process.
+    ///
+    /// @return true if the sender has at IO ready, false otherwise.
     virtual bool ioReady() = 0;
 
 protected:

src/lib/dhcp_ddns/ncr_udp.h

@@ -542,6 +542,9 @@ public:
     /// @throw NcrSenderError if the sender is not in send mode,
     virtual int getSelectFd();
 
+    /// @brief Returns whether or not the sender has IO ready to process.
+    ///
+    /// @return true if the sender has at IO ready, false otherwise.
     virtual bool ioReady();
 
 private: