batman-adv: don't initialise batman_iv private members in hard-interface.c

hard-interface.c has to do not contain any routing algorithm
specific code.

Allocate the hard-interface with kzalloc() and remove any
useless and algorithm specific member initialisation

Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>