sunvnet: remove extra rcu_read_unlocks

The RCU read lock is grabbed first thing in sunvnet_start_xmit_common()
so it always needs to be released.  This removes the conditional release
in the dropped packet error path and removes a couple of superfluous
calls in the middle of the code.

Reported-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>