Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

tests/sys/audit: Skip extattr tests if extattrs are not supported

In the CheriBSD CI, we run the testsuite with /tmp as tmpfs. This causes
the extattr audit tests to fail since tmpfs does not (yet) support
extattrs. Skip those tests if the target path is on a file system that
does not support extended file attributes.

While touching these two files also convert the ATF_REQUIRE_EQ(-1, ...)
checks to use ATF_REQURIE_ERRNO().

Reviewed By: asomers
Differential Revision: https://reviews.freebsd.org/D28392

audit(4): Add tests for the fr class of syscalls

readlink and readlinkat are the only syscalls in this class. open and
openat are as well, but they'll be handled in a different file. Also, tidy
up the copyright headers of recently added files in this area.

Submitted by: aniketp
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15636

Add initial set of tests for audit(4)

This change includes the framework for testing the auditability of various
syscalls, and includes changes for the first 12. The tests will start
auditd(8) if needed, though they'll be much faster if it's already running.
The syscalls tested in this commit include mkdir(2), mkdirat(2), mknod(2),
mknodat(2), mkfifo(2), mkfifoat(2), link(2), linkat(2), symlink(2),
symlinkat(2), rename(2), and renameat(2).

Submitted by: aniketp
MFC after: 2 weeks
Sponsored by: Google, Inc (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15286