selftests/bpf: add selftest part of "bpf: improve verifier branch analysis"

Backport the missing selftest part of commit 7da6cd69 ("bpf: improve
verifier branch analysis") in order to fix the following test_verifier
failures:

...
Unexpected success to load!
0: (b7) r0 = 0
1: (75) if r0 s>= 0x0 goto pc+1
3: (95) exit
processed 3 insns (limit 131072), stack depth 0
Unexpected success to load!
0: (b7) r0 = 0
1: (75) if r0 s>= 0x0 goto pc+1
3: (95) exit
processed 3 insns (limit 131072), stack depth 0
...

The changesets apply with a minor context difference.

Fixes: 7da6cd69

 ("bpf: improve verifier branch analysis")
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>