Call lc() when substitute a hostname or an IP address for $connheader

[azumakuniyuki]

% find lib -type f -exec grep connheader {} /dev/null \; | grep host

if( $e =~ m/\A[Rr]eporting-MTA:[ ]*(?:DNS|dns);[ ]*(.+)\z/ ) {
    # Reporting-MTA: dns; mx.example.jp
    next if length $connheader->{'lhost'};
   $connheader->{'lhost'} = $1;
   $connvalues++;