dnsmasq: add support for multiple tags for each host.

dnsmasq: add support for multiple tags for each host.

Currently, dnsmasq support assigning multiple tags to a host record
(--dhcp-host), but we only support only 1 tag for a host. The commit
makes the following config to be valid:

  config host
      option name 'computer'
      option mac '00:11:22:33:44:55'
      option ip '192.168.1.100'
      list tag 'vendor_class'
      list tag 'vendor_id'

  config tag 'vendor_class'
      list dhcp_option 'option:vendor-class,00:...<omitted>'

  config tag 'vendor_id'
      option force '1'
      list dhcp_option 'option:vendor-id-encap,00:...<omitted>'

Signed-off-by: Kuang Rufan <kuangrufan@pset.suntec.net>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>