net: qualcomm: rmnet: Fix leak on transmit failure

[ Upstream commit c20a548792f15f8d8e38cd74356301c6db0d241f ]

If a skb in transmit path does not have sufficient headroom to add
the map header, the skb is not sent out and is never freed.

Fixes: ceed73a2 ("drivers: net: ethernet: qualcomm: rmnet: Initial implementation")
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>