sandbox: permit listen(2)

Fix for 12115; bugfix on 0.2.5.1-alpha

changes/bug12115

@@ -0,0 +1,3 @@
+  o Minor bugfixes (linux seccomp sandbox):
+    - Avoid crashing when re-opening listener ports with the seccomp
+      sandbox active. Fixes bug 12115; bugfix on 0.2.5.1-alpha.

src/common/sandbox.c

@@ -186,6 +186,7 @@ static int filter_nopar_gen[] = {
 
     // socket syscalls
     SCMP_SYS(bind),
+    SCMP_SYS(listen),
     SCMP_SYS(connect),
     SCMP_SYS(getsockname),
     SCMP_SYS(recvmsg),