1) Allow the sending of more than one control message at a time
over a unix domain socket. This should cover the PR 29499.
2) This requires that unp_{ex,in}ternalize and unp_scan understand
mbufs with more than one control message at a time.
3) Internalize and externalize used to work on the mbuf in-place.
This made life quite complicated and the code for sizeof(int) <
sizeof(file *) could end up doing the wrong thing. The patch always
create a new mbuf/cluster now. This resulted in the change of the
prototype for the domain externalise function.
4) You can now send SCM_TIMESTAMP messages.
5) Always use CMSG_DATA(cm) to determine the start where the data
in unp_{ex,in}ternalize. It was using ((struct cmsghdr *)cm + 1)
in some places, which gives the wrong alignment on the alpha.
(NetBSD made this fix some time ago).
This results in an ABI change for discriptor passing and creds
passing on the alpha. (Probably on the IA64 and Spare ports too).
6) Fix userland programs to use CMSG_* macros too.
7) Be more careful about freeing mbufs containing (file *)s.
This is made possible by the prototype change of externalise.
PR: 29499
MFC after: 6 weeks
2bc21ed985