Add start_tls_s() comment and use DataFlow::MethodCallNode instead

Author: jorgectf

python/ql/src/experimental/semmle/python/frameworks/LDAP.qll

@@ -116,9 +116,9 @@ private module LDAP {
           (
             // ldap_connection.start_tls_s()
             // see https://www.python-ldap.org/en/python-ldap-3.3.0/reference/ldap.html#ldap.LDAPObject.start_tls_s
-            exists(DataFlow::AttrRead startTLS |
+            exists(DataFlow::MethodCallNode startTLS |
               startTLS.getObject().getALocalSource() = initialize and
-              startTLS.getAttributeName() = "start_tls_s"
+              startTLS.getMethodName() = "start_tls_s"
             )
             or
             // ldap_connection.set_option(ldap.OPT_X_TLS_%s, True)
@@ -221,8 +221,10 @@ private module LDAP {
               .flowsTo([serverCall.getArg(2), serverCall.getArgByName("use_ssl")])
         )
         or
-        exists(DataFlow::AttrRead startTLS |
-          startTLS.getAttributeName().matches("%start_tls%") and
+        // ldap_connection.start_tls_s()
+        // see https://www.python-ldap.org/en/python-ldap-3.3.0/reference/ldap.html#ldap.LDAPObject.start_tls_s
+        exists(DataFlow::MethodCallNode startTLS |
+          startTLS.getMethodName() = "start_tls_s" and
           startTLS.getObject().getALocalSource() = this
         )
       }