net: Handle different key sizes between address families in flow cache

commit aa1c366e4febc7f5c2b84958a2dd7cd70e28f9d0 upstream.

With the conversion of struct flowi to a union of AF-specific structs, some
operations on the flow cache need to account for the exact size of the key.

Signed-off-by: David Ward <david.ward@ll.mit.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>