selftests/seccomp: Actually sleep for 1/10th second

Clang noticed that some none-zero sleep()s were actually using zero
anyway. This switches to nanosleep() to gain sub-second granularity.

seccomp_bpf.c:2625:9: warning: implicit conversion from 'double' to
      'unsigned int' changes value from 0.1 to 0 [-Wliteral-conversion]
                sleep(0.1);
                ~~~~~ ^~~

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Shuah Khan <shuah@kernel.org>