This patch adds a new OVN action 'put_dhcp_opts' to support native
DHCP in OVN.

ovn-controller parses this action and adds a NXT_PACKET_IN2
OF flow with 'pause' flag set and the DHCP options stored in
'userdata' field.

When the valid DHCP packet is received by ovn-controller, it frames a
new DHCP reply packet with the DHCP options present in the
'userdata' field and resumes the packet and stores 1 in the 1-bit subfield.
If the packet is invalid, it resumes the packet without any modifying and
stores 0 in the 1-bit subfield.

Eg. reg0[0] = put_dhcp_opts(offerip = 10.0.0.4, router = 10.0.0.1,
                  netmask = 255.255.255.0, lease_time = 3600,....)

A new 'DHCP_Options' table is added in SB DB which stores
the supported DHCP options with DHCP code and type. ovn-northd is
expected to popule this table.

The next patch will add logical flows with this action.

Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
Co-authored-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>