Fix zoneid when USER_NS is disabled
getzoneid() should return GLOBAL_ZONEID instead of 0 when USER_NS is disabled.
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ilkka Sovanto <github@ilkka.kapsi.fi>
Closes #15560