passt: Allow exit_group() system call in seccomp profiles

We handle SIGQUIT and SIGTERM calling exit(), which is usually
implemented with the exit_group() system call.

If we don't allow exit_group(), we'll get a SIGSYS while handling
SIGQUIT and SIGTERM, which means a misleading non-zero exit code.

Reported-by: Wenli Quan <wquan@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2101990
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

passt.c

@@ -257,6 +257,8 @@ static int sandbox(struct ctx *c)
  *
  * TODO: After unsharing the PID namespace and forking, SIG_DFL for SIGTERM and
  * SIGQUIT unexpectedly doesn't cause the process to terminate, figure out why.
+ *
+ * #syscalls exit_group
  */
 void exit_handler(int signal)
 {