Merge branch 'bpf-improve-verifier-state-analysis'

Alexei Starovoitov says:

====================
v1->v2:
With optimization suggested by Jakub patch 4 safety check became
cheap enough.

Several improvements to verifier state logic.
Patch 1 - trivial optimization
Patch 3 - significant optimization for stack state equivalence
Patch 4 - safety check for liveness and prep for future state merging
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>