update.sh: Fixes Bug#13137 - Existing n2n client connection created with openssl...

update.sh: Fixes Bug#13137 - Existing n2n client connection created with openssl-1.1.1x fails to start with openssl-3.x

- This modification will check if ovpnconfig exists and is not empty. If so then it will
   check for all n2n connections and if they are Client configs will check if
   "providers legacy default" is not already present and if so will add it.

Fixes: Bug#13137
Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>