dnsmasq: add UCI DNSSEC runtime support

Ship keys for the root zone and add two uci options to enable
DNSSEC checks:

Option 'dnssec': Activate DNSSEC validation
Option 'dnsseccheckunsigned': Ensure answers without DNSSEC are in
unsigned zones.

Signed-off-by: Andre Heider <a.heider@gmail.com>

SVN-Revision: 41245