bpftool: Add missing blank lines in bpftool-net doc example

In bpftool-net documentation, two blank lines are missing in a
recently added example, causing docutils to complain:

    $ cd tools/bpf/bpftool
    $ make doc
      DESCEND Documentation
      GEN     bpftool-btf.8
      GEN     bpftool-cgroup.8
      GEN     bpftool-feature.8
      GEN     bpftool-gen.8
      GEN     bpftool-iter.8
      GEN     bpftool-link.8
      GEN     bpftool-map.8
      GEN     bpftool-net.8
    <stdin>:189: (INFO/1) Possible incomplete section title.
    Treating the overline as ordinary text because it's so short.
    <stdin>:192: (INFO/1) Blank line missing before literal block (after the "::")? Interpreted as a definition list item.
    <stdin>:199: (INFO/1) Possible incomplete section title.
    Treating the overline as ordinary text because it's so short.
    <stdin>:201: (INFO/1) Blank line missing before literal block (after the "::")? Interpreted as a definition list item.
      GEN     bpftool-perf.8
      GEN     bpftool-prog.8
      GEN     bpftool.8
      GEN     bpftool-struct_ops.8

Add the missing blank lines.

Fixes: 0d7c06125cea ("bpftool: Add document for net attach/detach on tcx subcommand")
Signed-off-by: Quentin Monnet <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: qmonnet

docs/bpftool-net.rst

@@ -187,6 +187,7 @@ EXAMPLES
 |
 
 ::
+
       tc:
       lo(1) tcx/ingress tc_prog prog_id 29
 
@@ -197,4 +198,5 @@ EXAMPLES
 |
 
 ::
+
       tc: