Remove the FP_SOFTFP flag.  It wasn't used but was leftover from the
software x86 math emulator.
MFamd64: Explicitly initialize the mxcsr during npxinit().
MFamd64: Move extern declaration of _ucodesel and _udatasel to
<machine/md_var.h>
Fix a bug which prevented ND6_IFF_IFDISABLED flag from clearing when
the newly-added IPv6 address was /128.

PR:	188032
MFamd64: Add support for extended FPU states on i386.  This includes
support for AVX on i386.
- Similar to amd64, move the FPU save area out of the PCB and instead
  store saved FPU state in a variable-sized buffer after the PCB on the
  stack.
- To support the variable PCB location, alter the locore code to only use
  the bottom-most page of proc0stack for init386().  init386() returns
  the correct stack pointer to locore which adjusts the stack for thread0
  before calling mi_startup().
- Don't bother setting cr3 in thread0's pcb in locore before calling
  init386().  It wasn't used (init386() overwrote it at the end) and
  it doesn't work with the variable-sized FPU save area.
- Remove the new-bus attachment from npx.  This was only ever useful for
  external co-processors using IRQ13, but those have not been supported
  for several years.  npxinit() is now called much earlier during boot
  (init386()) similar to amd64.
- Implement PT_{GET,SET}XSTATE and I386_GET_XFPUSTATE.
- npxsave() is now only called from context switch contexts so it can
  use XSAVEOPT.

Differential Revision:	https://reviews.freebsd.org/D1058
Reviewed by:	kib
Tested on:	FreeBSD/i386 VM under bhyve on Intel i5-2520
 - Make sure random_adaptor accesses happen only when
   random_adaptors_lock is held.
 - Use sx_sleep instead of tsleep in read and write path to allow
   another thread that registers a new random adapter when waiting.
   Assert that random_adaptor is not NULL after reacquiring the lock.
 - Capture EINTR/ERESTART from sx_sleep to allow the blocking cycle be
   stopped when user requests so, while there also make short
   read/write's return 0.
 - Move M_WAITOK allocations out of lock scope.

In collobration with:	kib, markm, ian, jilles
Reviewed by:	kib, markm
Approved by:	so
Do not try to create a /dev/log symlink in a jail.

PR:	179828
Fix up some session-related races in devfs.

One was introduced with r272596, the rest was there to begin with.

Noted by: jhb
filedesc: create a dedicated zone for struct filedesc0

Currently sizeof(struct filedesc0) is 1096 bytes, which means allocations from
malloc use 2048 bytes.

There is no easy way to shrink the structure <= 1024 an it is likely to grow in
the future.
Don't assert random_adaptors_lock in random_adaptor_read_rate().

Reported by:	many
Pointy hat to:	delphij (for not testing the commit with WITNESS)
Approved by:	so
filedesc: plug unnecessary fdp NULL checks in fdescfreee and fdcopy

Anything reaching these functions has fd table.
Integrate usr.sbin/useradd/t_useradd.sh from NetBSD into FreeBSD as pw_test

- Suffix useradd/userdel commands with pw
- Remove the atf_expect_fail for bin/39546

Phabric: D921
Reviewed by: brd
Sponsored by: EMC / Isilon Storage Division