sr9700: use skb_cow_head() to deal with cloned skbs

sr9700: use skb_cow_head() to deal with cloned skbs

commit d532c1082f68176363ed766d09bf187616e282fe upstream.

We need to ensure there is enough headroom to push extra header,
but we also need to check if we are allowed to change headers.

skb_cow_head() is the proper helper to deal with this.

Fixes: c9b37458e956 ("USB2NET : SR9700 : One chip USB 1.1 USB2NET SR9700Device Driver Support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: James Hughes <james.hughes@raspberrypi.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>