cxgb4: add missing release on skb in uld_send()

[ Upstream commit e6827d1a ]

In the implementation of uld_send(), the skb is consumed on all
execution paths except one. Release skb when returning NET_XMIT_DROP.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>