net: Use device model to get driver name in skb_gso_segment()

ethtool operations generally require the caller to hold RTNL and are
not safe to call in atomic context.  The device model provides this
information for most devices; we'll only lose it for some old ISA
drivers.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>