scripts/download.pl: add support for adding mirrors through an environment variable

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43654 3c298f89-4303-0410-b956-a3cf2f4a3e73

scripts/download.pl

@@ -40,6 +40,9 @@ sub localmirrors {
 		close CONFIG;
 	};
 
+	my $mirror = $ENV{'DOWNLOAD_MIRROR'};
+	$mirror and push @mlist, split(/;/, $mirror);
+
 	return @mlist;
 }