- Implement two new system calls:

	int bindat(int fd, int s, const struct sockaddr *addr, socklen_t addrlen);
	int connectat(int fd, int s, const struct sockaddr *name, socklen_t namelen);

  which allow to bind and connect respectively to a UNIX domain socket with a
  path relative to the directory associated with the given file descriptor 'fd'.

- Add manual pages for the new syscalls.

- Make the new syscalls available for processes in capability mode sandbox.

- Add capability rights CAP_BINDAT and CAP_CONNECTAT that has to be present on
  the directory descriptor for the syscalls to work.

- Update audit(4) to support those two new syscalls and to handle path
  in sockaddr_un structure relative to the given directory descriptor.

- Update procstat(1) to recognize the new capability rights.

- Document the new capability rights in cap_rights_limit(2).

Sponsored by:	The FreeBSD Foundation
Discussed with:	rwatson, jilles, kib, des
Regen after r247667.
Add support for bindat(2) and connectat(2).

Sponsored by:	The FreeBSD Foundation
MFcalloutng:
Give OFED Linux wrapper own "expires" field instead of abusing callout's
c_time, which will change its type and units with calloutng commit.
Polish few spaces/tabs.
Add protective parentheses for macro argument, missed in r247671.