Add a minimal length to the national significant number, in order to identify the national short numbers that do not require the international prefix.
Mantis : 0012700: Short numbers : don't prefix called number with CC https://mantis.linphone.org/view.php?id=12700
Jira : SDK-214 Numéros de téléphone courts sans préfixe https://linphone.atlassian.net/browse/SDK-214