dnsmasq: respect option dhcpv4 disabled in dhcp-config

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42216 3c298f89-4303-0410-b956-a3cf2f4a3e73
odhcpd: various DHCPv4 and DHCPv6 fixes

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42217 3c298f89-4303-0410-b956-a3cf2f4a3e73