tools/rtla: Generate optstring from long options

tools/rtla: Generate optstring from long options

getopt_long() processes short and long options independently.
RTLA, like the majority of applications, uses both short and long
variants for each logical option.

Since the val member of struct option holds the letter of the short
variant, the string of short options can be reconstructed from the
array of long options.

Add getopt_auto() to generate optstring from an array of long options,
eliminating the need to maintain separate short option strings.

Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Reviewed-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260108095011.2115719-1-costa.shul@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>