libbeauty: Introduce syscall_arg__strtoul_strarrays()

To allow going from string to integer for 'struct strarrays'.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-b1ia3xzcy72hv0u4m168fcd0@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>