Apply upstream 13597:3eac1e8e0f4c (git: illumos-gate@aa846ad9):

Initialize tqent_flags in the userland taskq implementation.  Without
this the assertion of tq->tq_freelist != NULL may fail in taskq_destroy.

The problem is that tqent_flags is never initialized in the userland
implementation while the kernel one does initialize it.  Without proper
initialization, the flag may have its lowest bit set, making it treated
as TQENT_FLAG_PREALLOC and never removing taskq_ent_t from tq_freelist.

MFC after:	2 weeks
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/hardening
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/segvguard
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/ptrace
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/log
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/userlandenhanced
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/chacha
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/pie
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/aout
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/hardening' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/segvguard' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/ptrace' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/log' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/userlandenhanced' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/pie' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/chacha' into hardened/current/unstable
Merge remote-tracking branch 'origin/hardened/current/aout' into hardened/current/unstable