bpf, doc: Fix some invalid links in bpf_devel_QA.rst

There exist some errors "404 Not Found" when I click the link
of "MAINTAINERS" [1], "samples/bpf/" [2] and "selftests" [3]
in the documentation "HOWTO interact with BPF subsystem" [4].

As Alexei Starovoitov suggested, just remove "MAINTAINERS" and
"samples/bpf/" links and use correct link of "selftests".

  [1] https://www.kernel.org/doc/html/MAINTAINERS
  [2] https://www.kernel.org/doc/html/samples/bpf/
  [3] https://www.kernel.org/doc/html/tools/testing/selftests/bpf/
  [4] https://www.kernel.org/doc/html/latest/bpf/bpf_devel_QA.html

Fixes: 5422283 ("bpf, doc: convert bpf_devel_QA.rst to use RST formatting")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Link: https://lore.kernel.org/bpf/1619062560-30483-1-git-send-email-yangtiezhu@loongson.cn

Documentation/bpf/bpf_devel_QA.rst

@@ -29,7 +29,7 @@ list:
 This may also include issues related to XDP, BPF tracing, etc.
 
 Given netdev has a high volume of traffic, please also add the BPF
-maintainers to Cc (from kernel MAINTAINERS_ file):
+maintainers to Cc (from kernel ``MAINTAINERS`` file):
 
 * Alexei Starovoitov <ast@kernel.org>
 * Daniel Borkmann <daniel@iogearbox.net>
@@ -234,21 +234,21 @@ be subject to change.
 
 Q: samples/bpf preference vs selftests?
 ---------------------------------------
-Q: When should I add code to `samples/bpf/`_ and when to BPF kernel
-selftests_ ?
+Q: When should I add code to ``samples/bpf/`` and when to BPF kernel
+selftests_?
 
 A: In general, we prefer additions to BPF kernel selftests_ rather than
-`samples/bpf/`_. The rationale is very simple: kernel selftests are
+``samples/bpf/``. The rationale is very simple: kernel selftests are
 regularly run by various bots to test for kernel regressions.
 
 The more test cases we add to BPF selftests, the better the coverage
 and the less likely it is that those could accidentally break. It is
 not that BPF kernel selftests cannot demo how a specific feature can
 be used.
 
-That said, `samples/bpf/`_ may be a good place for people to get started,
+That said, ``samples/bpf/`` may be a good place for people to get started,
 so it might be advisable that simple demos of features could go into
-`samples/bpf/`_, but advanced functional and corner-case testing rather
+``samples/bpf/``, but advanced functional and corner-case testing rather
 into kernel selftests.
 
 If your sample looks like a test case, then go for BPF kernel selftests
@@ -645,10 +645,9 @@ when:
 
 .. Links
 .. _Documentation/process/: https://www.kernel.org/doc/html/latest/process/
-.. _MAINTAINERS: ../../MAINTAINERS
 .. _netdev-FAQ: ../networking/netdev-FAQ.rst
-.. _samples/bpf/: ../../samples/bpf/
-.. _selftests: ../../tools/testing/selftests/bpf/
+.. _selftests:
+   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/
 .. _Documentation/dev-tools/kselftest.rst:
    https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html
 .. _Documentation/bpf/btf.rst: btf.rst