sky2: use new netdev_rss_key_fill() helper

Switch to a random RSS key rather than a fixed one.
Using netdev_rss_key_fill helper also ensures that all ports share
a common key.

See also commit 960fb622.

Signed-off-by: Ian Morris <ipm@chirality.org.uk>
Cc: Mirko Lindner <mlindner@marvell.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Eric Dumazet <edumazet@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>