Staging: batman-adv: Use forw_bcast_list_lock always with disabled interrupts

forw_bcast_list_lock is spin_locked in both process and softirq context.
SoftIRQ calls the spinlock with disabled IRQ and normal process context
with enabled IRQs.

When process context is inside an spin_locked area protected by
forw_bcast_list_lock and gets interrupted by an IRQ, it could happen
that something tries to lock forw_bcast_list_lock again in SoftIRQ
context. It cannot proceed further since the lock is already taken
somewhere else, but no reschedule will happen inside the SoftIRQ
context. This leads to an complete kernel hang without any chance of
resurrection.

All functions called in process context must disable IRQs when they try
to get get that lock to to prevent any reschedule due to IRQs.

Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.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>