selftests/bpf: Update LLVM Phabricator links

reviews.llvm.org was LLVM's Phabricator instances for code review. It
has been abandoned in favor of GitHub pull requests. While the majority
of links in the kernel sources still work because of the work Fangrui
has done turning the dynamic Phabricator instance into a static archive,
there are some issues with that work, so preemptively convert all the
links in the kernel sources to point to the commit on GitHub.

Most of the commits have the corresponding differential review link in
the commit message itself so there should not be any loss of fidelity in
the relevant information.

Additionally, fix a typo in the xdpwall.c print ("LLMV" -> "LLVM") while
in the area.

Link: https://discourse.llvm.org/t/update-on-github-pull-requests/71540/172


Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20240111-bpf-update-llvm-phabricator-links-v2-1-9a7ae976bd64@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>