use #!/usr/bin/env perl instead of #!/usr/bin/perl in openwrt scripts (fixes #2998)

use #!/usr/bin/env perl instead of #!/usr/bin/perl in openwrt scripts (fixes #2998)

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@12674 3c298f89-4303-0410-b956-a3cf2f4a3e73