Merge from projects/sendfile:

o Provide a new VOP_GETPAGES_ASYNC(), which works like VOP_GETPAGES(), but
  doesn't sleep. It returns immediately, and will execute the I/O done handler
  function that must be supplied as argument.
o Provide VOP_GETPAGES_ASYNC() for the FFS, which uses vnode_pager.
o Extend pagertab to support pgo_getpages_async method, and implement this
  method for vnode_pager.

Reviewed by:	kib
Tested by:	pho
Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
Don't use the synchronization endpoint unless referenced by the
isochronous endpoint descriptor used for the data transfers, hence the
synchronization feature might not be supposed to be supported [yet].
This makes seamless playback synced with the USB HOST clock work with
the DN32-USB module for Midas audio systems and possibly other similar
products from Klark Teknik.

MFC after:	1 week
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
HBSD: drop unused variables from hardening_features structure

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: refactor kern/kern_pax.c -> hardenedbsd/hbsd_pax_common.c

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: refactor: kern/kern_pax_aslr.c -> hardenedbsd/hbsd_pax_aslr.c

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>
HBSD: refacor: kern/kern_pax_hardening.c -> hardenedbsd/hbsd_pax_hardening.c

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: refactor: kern/kern_pax_segvguard.c -> hardenedbsd/hbsd_pax_segvguard.c

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: refactor kern/kern_hardening_log.c -> hardenedbsd/hbsd_pax_log.c

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: refactor: kern/kern_ptrace_hardening.c -> hardenedbsd/hbsd_ptrace_hardening.c

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: refactor opt_ptrace_hardening.h -> opt_pax.h

github-issue: #60
Signed-off-by: Oliver Pinter <oliver.pinter@hardenedbsd.org>
HBSD: fix fatal error in ptrace hardening

op@opn sys> git grep PTRACE_HARDENING_MODE_ROOTONLY
sys/ptrace_hardening.h:#define PTRACE_HARDENING_MODE_ROOTONLY   0x0
hardenedbsd/hbsd_ptrace_hardening.c:                    flags |=PTRACE_HARDENING_MODE_ROOTONLY;

ergo flags |= 0 ...

github-issue: #60
CC: David Carlier <david.carlier@hardenedbsd.org>
Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>