Log Message:
lsof: fix builds on NetBSD as of 9.99.93 on 2022-01-17

procfs.h had an inline function added that expects curlwp to be
defined. It isn't needed by this code base, and I don't see any other
way of fixing this than adding a basic definition to get this to
compile. It looks "wrong", but this code base requires _KERNEL to be
defined when including procfs.h, but we can't include lwp.h or machine/
cpu.h with that defined, header files that aren't available to userland
get referenced and break the build that way, instead.