extprotocol: fix option parsing in check_ext_options
extprotocol: fix option parsing in check_ext_options

When this code was added (commit 210ab15e), it treated the
ExtTableEntry.options member as a List of DefElems. It's actually a List
of Values (specifically, T_Strings). This code will break when the
offset of DefElem.defname changes in the upcoming 8.4 merge iteration.

50wu/gpdb,jmcatamney/gpdb,edespino/gpdb,yuanzhao/gpdb,Chibin/gpdb,jmcatamney/gpdb,Chibin/gpdb,edespino/gpdb,lisakowen/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,adam8157/gpdb,50wu/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,xinzweb/gpdb,Chibin/gpdb,jmcatamney/gpdb,Chibin/gpdb,Chibin/gpdb,lisakowen/gpdb,adam8157/gpdb,xinzweb/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,edespino/gpdb,xinzweb/gpdb,adam8157/gpdb,Chibin/gpdb,xinzweb/gpdb,adam8157/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,edespino/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,xinzweb/gpdb,greenplum-db/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,50wu/gpdb,ashwinstar/gpdb,Chibin/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,Chibin/gpdb,Chibin/gpdb,edespino/gpdb,greenplum-db/gpdb,edespino/gpdb,ashwinstar/gpdb,lisakowen/gpdb,edespino/gpdb,ashwinstar/gpdb,adam8157/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,edespino/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,ashwinstar/gpdb,50wu/gpdb,edespino/gpdb,edespino/gpdb,Chibin/gpdb,xinzweb/gpdb