bpf: fix validate for function return value

bpf: fix validate for function return value

eval_call() blindly calls eval_max_bound() for external function
return value for all return types.
That causes wrong estimation for returned pointer min and max boundaries.
So any attempt to dereference that pointer value causes verifier to fail
with error message: "memory boundary violation at pc: ...".
To fix - estimate min/max boundaries based on the return value type.

Bugzilla ID: 298

Fixes: 8021917293d0 ("bpf: add extra validation for input BPF program")
Cc: stable@dpdk.org
Reported-by: Michel Machado <michel@digirati.com.br>
Suggested-by: Michel Machado <michel@digirati.com.br>
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>