NETROM: Fix use of static buffer

The static variable used by nr_call_to_digi might result in corruption if
multiple threads are trying to usee a node or neighbour via ioctl.  Fixed
by having the caller pass a structure in.  This is safe because nr_add_node
rsp. nr_add_neigh will allocate a permanent structure, if needed.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>