bpf: move BPF_PROG_TYPE_FLOW_DISSECTOR documentation to a new common place

In commit da703149 ("bpf: Document BPF_PROG_TYPE_CGROUP_SYSCTL")
Andrey proposes to put per-prog type docs under Documentation/bpf/

Let's move flow dissector documentation there as well.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/bpf/index.rst

@@ -43,6 +43,7 @@ Program types
    :maxdepth: 1
 
    prog_cgroup_sysctl
+   prog_flow_dissector
 
 
 .. Links:

Documentation/networking/bpf_flow_dissector.rst → Documentation/bpf/prog_flow_dissector.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-==================
-BPF Flow Dissector
-==================
+============================
+BPF_PROG_TYPE_FLOW_DISSECTOR
+============================
 
 Overview
 ========

Documentation/networking/index.rst

@@ -9,7 +9,6 @@ Contents:
    netdev-FAQ
    af_xdp
    batman-adv
-   bpf_flow_dissector
    can
    can_ucan_protocol
    device_drivers/freescale/dpaa2/index