batman-adv: print the new BATADV_TT_CLIENT_ISOLA flag

Print the new BATADV_TT_CLIENT_ISOLA flag properly in the
Local and Global Translation Table output.

The character 'I' is used in the flags column to indicate
that the entry is marked as isolated.

Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>