After 5f0e9733 htonl was called twice: once before calling
dhcp_mbuf::compose_request and once more inside this function.
Fix this, verified on wire packets with wireshark and audited code.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>

Some IP fields are stored in host order and some other in network order.
It makes discovery of the code difficult.
Convert all IP fields to host order and propagate to callers.

Signed-off-by: Benoit Canet <benoit@irqsave.net>

Added Cloudius copyright statement to core/*.

poll.cc already had a BSD copyright statement, I believe this is a mistake
(I think Guy wrote this code from scratch), but not wanting to rush to a
conclusion I'm leaving both copyright statements and we should address this
issue later.

Rarely (about once every 20 runs) we had OSV crash during boot, in the
DHCP code. It turns out that the code first sends out the DCHP requests,
and then creates a thread to handle the replies. When a reply arrives,
the code wake()s the thread, but on rare occasions the thread hasn't yet
been set up (still a null pointer) so we have a crash.

Fix this by reversing the order - first create the reply handling thread,
and only then send the request.

the QEMU DHCP server responds with broadcast packets; allow them.

We don't initialize the dhcp packets, so some of them get the relay agent IP
set, and the DHCP DISCOVER packets get sent to a random address on the
Internet.  Usually it doesn't have a DHCP server installed, so the guest
does not get configured.

Fix by zero-initializing the packet.

M_ZERO requests zeroing of the entire mbuf, which clears the fields initialized
by the init function.  It only works now because we don't honor M_ZERO.

Remove M_ZERO and replace with bzero() for the packet data only.

Use DHCP to discover an IP address per each interface, DHCP packets are being hooked
in the networking stack in ip_input and queued for deffered processing using a
dhcp worker thread. Sending dhcp packet is done directly over ethrernet (building
IP and UDP).

There's still alot to be done: setting up lease time, timeouts, more error handling
but it's possible to implement these later on.