Staging: batman-adv: Fixes rounding issues in vis.c

This patches fixes two rounding issues in vis.c for sending and
purging vis packets. Before, the timers and timeouts always got
rounded down to seconds, though we want a precision in
milliseconds.

This also fixes a kernel panic that occures when lowering the
timer for sending vis packets (vis_interval) to less than 1000ms
in main.c manually.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Acked-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>