selftests/bpf: Improve recursion selftest

Since recursion_misses counter is available in bpf_prog_info
improve the selftest to make sure it's counting correctly.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210210033634.62081-8-alexei.starovoitov@gmail.com