Gave asynchronous operations approximate POSIX signal semantics. This
will enable us to cascade async operations, which is necessary in order to
properly support DNS. (For example, an HTTP request may have to redirect
to a new location and will have to perform a new DNS lookup, so we can't
just rely on doing the name lookup at the time of parsing the initial
URL).
Anything other than HTTP is probably broken right now; I'll fix the others
up asap.
Split DHCP packet creation into two parts: creating the basic packet
structure, and populating it with options. This should allow us to
use the same basic options list for both DHCPDISCOVER and DHCPREQUEST,
plus making it much easier to set the non-constant parameters
(e.g. requested IP address) in request packets.
Allow for calling find_dhcp_option() with "options" set to NULL, in order
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.
Add sketch code to reassemble a DHCP packet from our internal "everything
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.