Disable TX IP header checksum offloading on RL_HWREV_8168CP. The
controller generates wrong checksummed frame if the IP packet has
IP options.

Submitted by:	Alexander Bluhm via brad@openbsd
Fix incorrect assertion that caused panic when periodic-only timers used.
Unlike OpenBSD's, our setusercontext() will intentionally ignore the user's
own umask setting (from ~/.login.conf) unless running with the user's UID.
Therefore, we need to call it again with LOGIN_SETUMASK after changing UID.

PR:		bin/176740
Submitted by:	John Marshall <john.marshall@riverwillow.com.au>
MFC after:	1 week
- Make the FreeBSD's USB library compile under Linux.
- Fix a compile warning where the return value of a call
to a write() function was ignored.
- Remove redundant include files from userland USB header files.
- Add some now needed include files to various C-files.
- Make quirk for reading device descriptor from broken USB devices.
Else they won't enumerate at all:
hw.usb.full_ddesc=1
- Reduce the USB descriptor read timeout from 1000ms to
500ms. Typical value for LOW speed devices is 50-100ms.
- Enumerate USB device a maximum of 3 times when a port
connection change event is detected, before giving up.

MFC after:	1 month
Fix typo.
Add the getcontextx prototype to SYNOPSIS.

Reviewed by:	kib
MFC after:	1 week
Link getcontextx(3) to getcontext(3).

Reviewed by:	kib
MFC after:	1 week
libc: Avoid SIGPIPE when nscd closes the connection unexpectedly.

It is almost always a bug if nscd closes the connection unexpectedly but
programs should not be killed with SIGPIPE for it.

Reviewed by:	bushman
Tested by:	Jan Beich
MFC after:	1 week
Add missed `_load' to the `if_foo_load="YES"' line.

PR:		docs/176915
MFC after:	1 week
Add quirk for Lenovo T530 headphone redirection.

MFC after:	2 weeks
Revert 195703 and 195821 as this special stop handling in NFS is now
implemented via VFCF_SBDRY rather than passing PBDRY to individual
sleep calls.
- Fix two possible overflows when testing if ELF program headers are on
  the first page:
  1. Cast uint16_t operands in a multiplication to unsigned int because
     otherwise the implicit promotion to int results in a signed
     multiplication that can overflow and the behaviour on integer
     overflow is undefined.
  2. Replace (offset + size > PAGE_SIZE) with (size > PAGE_SIZE - offset)
     because the sum may overflow.
- Use the same tests to see if the path to the interpreter is on the first
  page. There's no overflow here because size is already limited by
  MAXPATHLEN, but the compiler optimises the new tests better. Also fix an
  off-by-one error.
- Simplify tests to see if an ELF note program header is on the first page.
  This also fixes an off-by-one error.

Reviewed by:	kib
MFC after:	1 week
vinum isn't a new product.
No need to call an external program.
Disable warning/errors for two files for now - they don't compile clean
with clang.

I'll work on this soon.
Merge branch 'master' into markj