I hope you don't mind if I go beyond what you asked about. (In fact, I won't even touch that since it's already been addressed.)

• Your parser accepts 127.   0.    0    .1 as a valid ip.
• Your parser accepts 127.newline0.newline0newline.1 as a valid ip.
• Your parser accepts 127.00000000000000.000000000000000.000000001 as a valid ip.
• Your parser accepts "newlineabcnewline" as a valid filename.
• Your parser returns abc for filename "   abc   ".
• Your parser accepts ip127.0.0.1 and tsig-keyserver.
• Your parser accepts bind-server 127.0.0.1 tsig-key "/etc/bind/rndc.key" all on one line. I'm pretty sure you don't want that.
• Using q{} around your grammar can easily lead to weird problems with slashes. You should double your slashes (yuck and easy to miss one) or use here-docs.
• <reject: do { ... }> can be simplified to <reject: ...>.
• strict and warnings aren't on for your actions and the parser in general.
• The return value for config shouldn't include $item[2].
• It's hard to see alternate rules. I line up the |s with the :s. (I also line up the :s, but that's personal preference.)
• What if the file name contains a "?
• I removed $::RD_AUTOACTION = q { [@item] };. It was causing extra code, not less.
• For the quoteless filename, it would be better if you specified which character *are* allowed.

use strict;
use warnings;

use Parse::RecDescent;
use Data::Dumper;

my $config_parser = Parse::RecDescent->new(<<'__END_OF_GRAMMAR__');

    {
       # These pragmas affect the whole parser.
       use strict;
       use warnings;

       sub check_ip_nums {
          my ($ip) = @_;
          return !(grep $_ > 255, split /./, $ip);
       }

       sub dequote {
          my ($s) = @_;
          for ($s) {
             s/^"//;
             s/"\z//;
             s/\\(.)/$1/sg;
             return $_;
          }
       }
    }


    parse      : line(s) /\Z/ { $item[1] }

    line       : ''                # Skip blank lines.
                 <skip:'[ \\t]*'>  # Don't treat newlines as whitespac
+e.
                 key_value /\n/
                 <skip: $item[2]>
                 { $item[3] }

    key_value  : server
               | key

    server     : IDENT { $item[1] eq 'bind-server' } IP { [@item[0,3]]
+ }

    key        : IDENT { $item[1] eq 'tsig-key' } filename { [@item[0,
+3]] }
    filename   : QSTRING
               | BAREWORD


    # Tokens

    IDENT      : /[-\w]+/
    QSTRING    : /"(?:[^"\\]|\\.)*"/ { dequote($item[1]) }
    BAREWORD   : /[^"\\\s]+/
    IP         : # This could be done more readably, but
                 # the more is done by the regexp, the
                 # faster it's going to be. A lot faster.
                 /(?:[1-9][0-9]{0,2}|0)\.(?:[1-9][0-9]{0,2}|0)\.(?:[1-
+9][0-9]{0,2}|0)\.(?:[1-9][0-9]{0,2}|0)/
                 { check_ip_nums($item[1]) ? $item[1] : undef }

__END_OF_GRAMMAR__


print Dumper $config_parser->parse(<<'__END_OF_CONFIG__');
    bind-server 127.0.0.1
    tsig-key "/etc/bind/rndc.key"
__END_OF_CONFIG__
[download]