Fix default EDNS behavior

This commit fixes queries defaulting as EDNS queries, which was unintended.
Documentation has been updated to reflect the new behavior.

lib/Zonemaster/Engine/Nameserver.pm

@@ -406,7 +406,13 @@ sub _query {
     $flags{q{fallback}}  = $href->{q{fallback}}  // Zonemaster::Engine::Profile->effective->get( q{resolver.defaults.fallback} );
     $flags{q{recurse}}   = $href->{q{recurse}}   // Zonemaster::Engine::Profile->effective->get( q{resolver.defaults.recurse} );
     $flags{q{timeout}}   = $href->{q{timeout}}   // Zonemaster::Engine::Profile->effective->get( q{resolver.defaults.timeout} );
-    $flags{q{edns_size}} = $href->{q{edns_size}} // $UDP_EDNS_QUERY_DEFAULT;
+
+    if ( $flags{q{dnssec}} ) {
+        $flags{q{edns_size}} = $href->{q{edns_size}} // $UDP_EDNS_QUERY_DEFAULT;
+    }
+    else {
+        $flags{q{edns_size}} = $href->{q{edns_size}} // 0;
+    }
 
     if ( exists $href->{edns_details} ) {
         $flags{q{dnssec}}    = $href->{edns_details}{do} // $flags{q{dnssec}};
@@ -794,7 +800,7 @@ The retransmission interval.
 Set the DO flag in the query. Defaults to false.
 
 If set to true, it becomes an EDNS query.
-Value overridden by 'edns_details->do' (if also given). More details in 'edns_details' below.
+Value overridden by C<edns_details{do}> (if also given). More details in L<edns_details> below.
 
 =item debug
 
@@ -826,10 +832,10 @@ If set to true, prevents a server to be black-listed on a query in case there is
 
 =item edns_size
 
-Set the EDNS0 UDP maximum size. Defaults to 512.
+Set the EDNS0 UDP maximum size. Defaults to 0, or 512 if the query is an EDNS query.
 
-Used only when the query is an EDNS query. Does not enable on its own the query to be an EDNS query.
-Value overridden by 'edns_details->size' (if also given). More details in 'edns_details' below.
+Setting a value other than 0 will also implicitly enable the query to be an EDNS query.
+Value overridden by C<edns_details{size}> (if also given). More details in L<edns_details> below.
 
 =item edns_details
 
@@ -838,10 +844,10 @@ A hash. An empty hash or a hash with any keys below will enable the query to be
 The currently supported keys are 'version', 'z', 'do', 'rcode', 'size' and 'data'.
 See L<Zonemaster::LDNS::Packet> for more details (key names prefixed with 'edns_').
 
-Note that flag 'edns_size' also exists (see above) and has the same effect as 'edns_details->size', although the value of the 
+Note that flag L<edns_size> also exists (see above) and has the same effect as C<edns_details{size}>, although the value of the
 latter will take precedence if both are given.
 
-Similarly, note that flag 'dnssec' also exists (see above) and has the same effect as 'edns_details->do', although the value of the
+Similarly, note that flag L<dnssec> also exists (see above) and has the same effect as C<edns_details{do}>, although the value of the
 latter will take precedence if both are given.
 
 =back