decode: Change return type of IPv4 and TCP options decode

decode: Change return type of IPv4 and TCP options decode

The return value from the options decoder in TCP and IPv4 is ignored.
This commit changes the return type of the function to `void` and
modifies existing return points to return without a value.

When an error occurs, the packet state is being set to indicate whether
it's valid or not and the existing return value is never used.