bootp: Add processing DHCPACK packet from HTTP Boot

bootp: Add processing DHCPACK packet from HTTP Boot

The vendor class identifier with the string "HTTPClient" is used to denote the
packet as responding to HTTP boot request. In DHCP4 config, the filename for
HTTP boot is the URL of the boot file while for PXE boot it is the path to the
boot file. As a consequence, the next-server becomes obseleted because the HTTP
URL already contains the server address for the boot file. For DHCP6 config,
there's no difference definition in existing config as dhcp6.bootfile-url can
be used to specify URL for both HTTP and PXE boot file.

This patch adds processing for "HTTPClient" vendor class identifier in DHCPACK
packet by treating it as HTTP format, not as the PXE format.

Signed-off-by: Michael Chang <mchang@suse.com>
Signed-off-by: Ken Lin <ken.lin@hpe.com>
Patch-Name: bootp_process_dhcpack_http_boot.patch