UBUNTU: SAUCE: Fix "bpf: improve verifier branch analysis"

UBUNTU: SAUCE: Fix "bpf: improve verifier branch analysis"

BugLink: https://launchpad.net/bugs/1841704
The upstream linux-stable backport of commit 4f7b3e82589e ("bpf: improve
verifier branch analysis") dropped the changes to the bpf selftests
which caused new test failures.

Fix the new test failures by making the .errstr and BPF_JMP_IMM()
changes from commit 4f7b3e82589e ("bpf: improve verifier branch
analysis").

Also, make the .errstr_unpriv change from commit 80c9b2fae87b ("bpf: add
various test cases to selftests"). That change was previously dropped
from my backport of that commit because we didn't backport commit
4f7b3e82589e at that time.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>