net: Use a more standard macro for INET_ADDR_COOKIE

Missing a colon on definition use is a bit odd so
change the macro for the 32 bit case to declare an
__attribute__((unused)) and __deprecated variable.

The __deprecated attribute will cause gcc to emit
an error if the variable is actually used.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>