[2656] Add using statements for createNameFromLexer()

This used to work before (without the using statement) as they
came after SOA in the generated files.

src/lib/dns/rdata/generic/mx_15.cc

@@ -31,6 +31,7 @@
 using namespace std;
 using boost::lexical_cast;
 using namespace isc::util;
+using isc::dns::rdata::generic::detail::createNameFromLexer;
 
 // BEGIN_ISC_NAMESPACE
 // BEGIN_RDATA_NAMESPACE

src/lib/dns/rdata/generic/ns_2.cc

@@ -26,6 +26,7 @@
 
 using namespace std;
 using namespace isc::util;
+using isc::dns::rdata::generic::detail::createNameFromLexer;
 
 // BEGIN_ISC_NAMESPACE
 // BEGIN_RDATA_NAMESPACE

src/lib/dns/rdata/generic/ptr_12.cc

@@ -22,8 +22,11 @@
 #include <dns/rdata.h>
 #include <dns/rdataclass.h>
 
+#include <dns/rdata/generic/detail/lexer_util.h>
+
 using namespace std;
 using namespace isc::util;
+using isc::dns::rdata::generic::detail::createNameFromLexer;
 
 // BEGIN_ISC_NAMESPACE
 // BEGIN_RDATA_NAMESPACE