net: make in_aton() 32-bit internally

Converting IPv4 address doesn't need 64-bit arithmetic.

Space savings: 10 bytes!

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-10 (-10)
	function                          old     new   delta
	in_aton                            96      86     -10

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>