Documentation: link in networking docs

Fix link in filter.txt.
Acked-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/filter.txt

@@ -45,7 +45,7 @@ in many more places. There's xt_bpf for netfilter, cls_bpf in the kernel
 qdisc layer, SECCOMP-BPF (SECure COMPuting [1]), and lots of other places
 such as team driver, PTP code, etc where BPF is being used.
 
- [1] Documentation/prctl/seccomp_filter.txt
+ [1] Documentation/userspace-api/seccomp_filter.rst
 
 Original BPF paper: