Fix ZTS killed processes detection

log_neg_expect was using the wrong exit status to detect if a process
got killed by SIGSEGV or SIGBUS, resulting in false positives.

Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Attila Fülöp <attila@fueloep.org>
Closes openzfs#9003

tests/test-runner/include/logapi.shlib

@@ -198,12 +198,12 @@ function log_neg_expect
 	elif (( $status == 127 )); then
 		print -u2 $($out)
 		_printerror "$@" "unexpectedly exited $status (File not found)"
-	# bus error - core dump
-	elif (( $status == 138 )); then
+	# bus error - core dump (256+signal, SIGBUS=7)
+	elif (( $status == 263 )); then
 		print -u2 $($out)
 		_printerror "$@" "unexpectedly exited $status (Bus Error)"
-	# segmentation violation - core dump
-	elif (( $status == 139 )); then
+	# segmentation violation - core dump (256+signal, SIGSEGV=11)
+	elif (( $status == 267 )); then
 		print -u2 $($out)
 		_printerror "$@" "unexpectedly exited $status (SEGV)"
 	else