Allow for settings to be described by something other than a DHCP option
tag if desirable.  Currently used only for the MAC address setting.

Separate out fake DHCP packet creation code from dhcp.c to fakedhcp.c.

Remove notion of settings from dhcppkt.c.

Rationalise dhcp.c to use settings API only for final registration of the
DHCP options, rather than using {store,fetch}_setting throughout.

Convert DHCP option applicators in dns.c and iscsi.c to settings
applicators.

Kill off DHCP option applicators.

not apply DHCP options in dhcp_configure_netdev().

Added test code to configure the interface for IPv4 after DHCP.

to search through all registered option blocks.

Move some static inlines that are likely to be used frequently into
dhcpopts.c as normal functions, to save space.

is a DHCP option" data structures.

We need this code in order to be able to return a DHCP packet to a PXE NBP
which reflects options from our multiple sources (e.g. NVS and DHCP
server).  This is expensive, but necessary.  Having paid this cost, we may
as well try to use the same code to generate our DHCP request packets,
since the process is similar.

encapsulated option; this will be needed for modifications to the options
block.

multiple option sources (e.g. multiple DHCP replies, non-volatile
storage etc.)