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: 54222838 ("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>
@@ -234,11 +234,11 @@ 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
@@ -246,9 +246,9 @@ 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