[3221] Fixed minor compilation errors in dhcp_ddns::WatchSocket

Compilation under Fedora turned a couple of missing includes,
errno.h and stdint.h.

src/lib/dhcp_ddns/watch_socket.cc

@@ -17,6 +17,8 @@
 #include <dhcp_ddns/dhcp_ddns_log.h>
 #include <dhcp_ddns/watch_socket.h>
 
+#include <errno.h>
+
 namespace isc {
 namespace dhcp_ddns {
 

src/lib/dhcp_ddns/watch_socket.h

@@ -21,6 +21,8 @@
 
 #include <boost/shared_ptr.hpp>
 
+#include <stdint.h>
+
 namespace isc {
 namespace dhcp_ddns {