aoe: remove dev_base_lock use from aoecmd_cfg_pkts()

dev_base_lock is the legacy way to lock the device list, and is planned
to disappear. (writers hold RTNL, readers hold RCU lock)

Convert aoecmd_cfg_pkts() to RCU locking.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Ed L. Cashin" <ecashin@coraid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>