Add dedicated functions create_dhcpdiscover(), create_dhcpack() and
create_proxydhcpack() for use by external code such as the PXE preboot
code.

Register ProxyDHCP options under the global scope "proxydhcp".

Unregister previously-acquired DHCP and ProxyDHCP settings when DHCP
succeeds.

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>

RFC 4390 provides for the DHCP client identifier to contain the link-layer
hardware type and MAC address when the MAC address exceeds 16 bytes.
However, the hardware type field is only 8 bits; we were assuming 16 bits.

separate xfer method.

Add missing .alloc_iob entries to several xfer_interface_operations
structures.

their equivalent DHCP-option-specified values.

also avoid waiting for ProxyDHCP offers).

Also reduce the ProxyDHCP timeout, because it's already irritating me.

to construct DHCP packets suitable for Infiniband.

to construct DHCP packets suitable for Infiniband.

to generate the initial transmission; this cuts off around 0.3s per
instantiated connection.

and generate DHCP options to indicate features to DHCP server (and to
PXE NBPs).

xfer_window() function, which can return a scalar rather than a
boolean.

not apply DHCP options in dhcp_configure_netdev().

begin with.

DHCPD and Windows RIS in particular).

attempt at triggering TCP-related protocols to start).

structures.

DHCP still broken and #if 0'd out.

output buffering defintions and the like)

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.

routing table entry just to fool ipv4.c any more.

defined in vsprintf.h.  (This may change, since vsprintf.h is a
non-standard name, but for now it's the one to use.)

There should be no need to include vsprintf.h just for DBG() statements,
since include/compiler.h forces it in for a debug build anyway.

list.

create_dhcp_packet() from pxe_preboot.c, after the dhcp_session is long
gone.

Expose the functions required by pxe_preboot.c

udp_connect() now follows the standard BSD sockets semantics and simply
sets the default address for outgoing packets; it doesn't filter incoming
packets.

Introduced struct sockaddr_tcpip, to simplify code that deals with
both IPv4 and IPv6 addresses.

Reorganised parts of tcpip.c and udp.c.