tc: m_xt: Prevent segfault with standard targets

Iptables standard targets like DROP or REJECT don't implement the print
callback in libxtables. Hence the following command would segfault:

| tc filter add dev d0 parent ffff: u32 match u32 0 0 action xt -j DROP

With this patch standard targets still can't be used (and are not really
useful anyway), but at least it doesn't crash anymore.

Signed-off-by: Phil Sutter <phil@nwl.cc>
1 file changed