Add default /etc/dnsmasq.conf

Add default /etc/dnsmasq.conf

dnsmasq allows adding of arbitrary SRV/PTR/TXT/CNAME records.
However, those options sometimes can not be passed as
command-line arguments due to excess length.  This patch tries to
solve this problem:

1. Provide /etc/dnsmasq.conf file with comments about adding
   SRV/PTR/TXT/CNAME records.
2. Add this file to conffiles list so it is preserver during
   backup/restore or system upgrade.

If someone needs a lot of custom records, default configuration
file can be edited.  Since manual pages and documentation is not
installed, provided comments should be enough to figure out
option syntax.

Signed-off-by: Alexey I. Froloff <raorn@altlinux.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@17663 3c298f89-4303-0410-b956-a3cf2f4a3e73