batman-adv: mark a local client as isolated when needed

A client sending packets which mark matches the value
configured via sysfs has to be identified as isolated using
the TT_CLIENT_ISOLA flag.

The match is mask based, meaning that only bits set in the
mask are compared with those in the mark value.

If the configured mask is equal to 0 no operation is
performed.

Such flag is then advertised within the classic client
announcement mechanism.

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