[2390] Add PTR implementation

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

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

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

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