net: ipv4: ip_input: fix blank line coding style issues

Fix blank line coding style issues, make the code cleaner.
Remove a redundant blank line in ip_rcv_core().
Insert a blank line in ip_rcv() between different statement blocks.

Signed-off-by: Yang Wei <yang.wei9@zte.com.cn>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>