[2390] Add NS implementation

src/lib/dns/gen-rdatacode.py.in

@@ -36,6 +36,7 @@ new_rdata_factory_users = [('aaaa', 'in'),
                            ('hinfo', 'generic'),
                            ('naptr', 'generic'),
                            ('mx', 'generic'),
+                           ('ns', 'generic'),
                            ('ptr', 'generic'),
                            ('soa', 'generic'),
                            ('spf', 'generic'),

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

@@ -39,6 +39,11 @@ NS::NS(InputBuffer& buffer, size_t) :
     // check consistency.
 }
 
+NS::NS(MasterLexer& lexer, const Name*, MasterLoader::Options,
+       MasterLoaderCallbacks&) :
+    nsname_(lexer.getNextToken(MasterToken::QSTRING).getString())
+{}
+
 NS::NS(const NS& other) :
     Rdata(), nsname_(other.nsname_)
 {}