Add an example that shows how to use kprobes and kretprobes with libbpf.
Describe the example in README.md.

Signed-off-by: Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>

Add an example that shows how to use fentry and fexit with
libbpf.
Describe the example in README.md.

Signed-off-by: Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>

Update submodule reference to the latest Github master commit.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Avoid dependency on up-to-date Linux UAPI headers (mainly linux/bpf.h and
linux/btf.h) by using headers distributed with libbpf for its own compilation
needs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Hook do_unlinkat() instead of bprm_execve() as bprm_execve() is a recent
kernel change.

Signed-off-by: Juraj Vijtiuk <juraj.vijtiuk@sartura.hr>

Positional or special parameters cannot be assigned using := way.