netlink_unicast() calls kfree_skb even in the error case.

dcbnl calls netlink_unicast() which when it fails free's the
skb and returns an error value.  dcbnl is free'ing the skb
again when this error occurs.  This patch removes the double
free.
Signed-off-by: NJohn Fastabend <john.r.fastabend@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>