no NET_RLOCK() for SIOCGIFCLONERS

[Theo Buehler]

This was pointed out to me by mpi a while ago.

The if_clone_list() function accesses &if_cloners, which is only
modified via if_clone_attach() and if_clone_detach().

The latter function is never called, as far as I can tell, while
if_clone_attach() is only called at boot time via the pdevinit[]
mechanism in ioconf.c.

So, for the purposes of the NET_LOCK(), &if_cloners is immutable, hence
if_clone_list() does not need the NET_RLOCK().

Index: sys/net/if.c
===================================================================
RCS file: /var/cvs/src/sys/net/if.c,v
retrieving revision 1.551
diff -u -p -r1.551 if.c
--- sys/net/if.c        28 Apr 2018 15:44:59 -0000      1.551
+++ sys/net/if.c        14 May 2018 07:37:01 -0000
@@ -2164,9 +2164,7 @@ ifioctl_get(u_long cmd, caddr_t data)
                NET_RUNLOCK();
                return (error);
        case SIOCIFGCLONERS:
-               NET_RLOCK();
                error = if_clone_list((struct if_clonereq *)data);
-               NET_RUNLOCK();
                return (error);
        case SIOCGIFGMEMB:
                NET_RLOCK();