mlxsw: spectrum: Fix memory leak at skb reallocation

During transmission the skb is checked for headroom in order to
add vendor specific header. In case the skb needs to be re-allocated,
skb_realloc_headroom() is called to make a private copy of the original,
but doesn't release it. Current code assumes that the original skb is
released during reallocation and only releases it at the error path
which causes a memory leak.

Fix this by adding the original skb release to the main path.

Fixes: 56ade8fe ("mlxsw: spectrum: Add initial support for Spectrum ASIC")
Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>