rtnetlink: switch rtnl_link_get_slave_info_data_size to rcu
David Ahern reports following splat:
RTNL: assertion failed at net/core/dev.c (5717)
netdev_master_upper_dev_get+0x5f/0x70
if_nlmsg_size+0x158/0x240
rtnl_calcit.isra.26+0xa3/0xf0
rtnl_link_get_slave_info_data_size currently assumes RTNL protection, but
there appears to be no hard requirement for this, so use rcu instead.
At the time of this writing, there are three 'get_slave_size' callbacks
(now invoked under rcu): bond_get_slave_size, vrf_get_slave_size and
br_port_get_slave_size, all return constant only (i.e. they don't sleep).
Fixes: 6853dd488119 ("rtnetlink: protect handler table with rcu") Reported-by: David Ahern <dsahern@gmail.com> Signed-off-by: Florian Westphal <fw@strlen.de> Acked-by: David Ahern <dsahern@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>