net: fix double skb free in dcbnl

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: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>