Change inet_sk_get_local_port_range() to return a boolean,
telling the callers if the port range was provided by
IP_LOCAL_PORT_RANGE socket option.

Adds documentation while we are at it.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20231214192939.1962891-2-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>