batman-adv: stop caching unowned originator pointers in BAT IV

In the Linux kernel, the following vulnerability has been resolved:

batman-adv: stop caching unowned originator pointers in BAT IV

BAT IV keeps the last-hop neighbor address in each neigh_node, but some

paths also cache an originator pointer derived from a temporary lookup.

That pointer is not owned by the neigh_node and may no longer refer to a

live originator entry after purge handling runs.

Stop storing the auxiliary originator pointer in the BAT IV neighbor

state. When BAT IV needs the neighbor originator data, resolve it from

the stored neighbor address and drop the reference again after use.

[sven: avoid bonding logic for outgoing OGM]