ksiginfo_alloc: pass M_WAITOK or M_NOWAIT to uma_zalloc

[vangyzen]

Summary

It expects exactly one of those flags. A future commit will assert this.

MFC after: 1 month
Sponsored by: Dell EMC Isilon

Test Plan

The whole kyua suite completed without a panic or a stack-dump like this (see D34452):

uma_zalloc_arg called with bad WAIT flags:
#0 0xffffffff80f72ca3 at uma_zalloc_arg+0x1a3
#1 0xffffffff80c207c6 at proc_linkup+0x26
#2 0xffffffff80bc0378 at fork1+0x408
#3 0xffffffff80bcf196 at kproc_create+0x96
#4 0xffffffff80bcf0dd at kproc_start+0x2d
#5 0xffffffff80b91a9f at mi_startup+0x20f
#6 0xffffffff80389022 at btext+0x22