[NET]: Move in_aton from net/ipv4/utils.c to net/core/utils.c

Move in_aton to allow netpoll and pktgen to work without the rest of
the IPv4 stack. Fix whitespace and add comment for the odd placement.

Delete now-empty net/ipv4/utils.c

Re-enable netpoll/netconsole without CONFIG_INET

Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>