dnsmasq currently permits dhcp_options to be specified only in "config dhcp"
sections of /etc/config/dhcp. When dnsmasq is providing DHCP service for
multiple subnets and there are multiple "config dhcp" sections without "option
ignore", it makes sense to allow dhcp_options that should apply globally in
the "config dnsmasq" section of /etc/config/dhcp. dhcp_option is a list option.

[jow: rework patch to apply after dhcp-option-force handling got introduced]

Signed-off-by: Mark Mentovai <mark@moxienet.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@32568 3c298f89-4303-0410-b956-a3cf2f4a3e73