selftests/bpf: Uprobe tests should verify param/return values

uprobe/uretprobe tests don't do any validation of arguments/return values,
and without this we can't be sure we are attached to the right function,
or that we are indeed attached to a uprobe or uretprobe.  To fix this
record argument and return value for auto-attached functions and ensure
these match expectations.  Also need to filter by pid to ensure we do
not pick up stray malloc()s since auto-attach traces libc system-wide.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1649245431-29956-4-git-send-email-alan.maguire@oracle.com