reconnection mechanism.  This avoids the problems of trying to reuse
the TCP connection structure before the old connection has cleanly exited.

TCP_CLOSED state (i.e. after the final FIN/ACK exchange), and has been
removed from the list of TCP connections.

Remove the now-totally-obsolete sockaddr_in field from tcp.h.

Added CHAP authentication

negotiation phases, to allow inclusion of CHAP authentication.

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.

against NULL.

already stopped.

Don't call start_timer() when sending a dataless ACK.  This may or may
not be the right thing to do; I can't tell.

Back out broken "send ACK only if required to" logic temporarily.

subsequent runs.

Use just random() to allocate initial sequence numbers; the previous
algorithm ended up with a high probability of zeroing the high word.

a TCP packet before passing to newdata().

stripping the header.  Also fix an htons/ntohs confusion.

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

Expose the functions required by pxe_preboot.c

Added a large number of missing calls to free_pkb().  In the case of UDP,
no received packets were ever freed, which lead to memory exhaustion
remarkably quickly once pxelinux started up.

In general, any function with _rx() in its name which accepts a pk_buff
*must* either call free_pkb() or pass the pkb to another _rx() function
(e.g. the next layer up the stack).  Since the UDP (and TCP) layers don't
pass packet buffers up to the higher-layer protocols (the
"applications"), they must free the packet buffer after calling the
application's newdata() method.