autodata: make note about not being generally useful for shared libraries.

If you have sections, it might still work for some cases though: on x86
Ubuntu it worked once I changed the section name from autodata to xautodata.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
list: list_append_list / list_prepend_list

Operations for moving the entire contents of a list.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
list: list_pop

list_top + list_del, as suggested by Ben Herrenschmidt.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
net: add server support.

Creating a server for IPv4 and IPv6 has similar issues to clients,
with some novel twists.  Slightly different arguments need to be given
to getaddrinfo(), but worse, some platforms (Linux without
/proc/sys/net/ipv6/bindv6only set) automatically bind IPv6 sockets to IPv4
ports as well.

Thus we need a function which can bind (and listen) to one or two fds.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>