drivers/net/arcnet/capmode.c: clean up code

 - shuffle around functions to get rid of forward declarations
 - fix some CodingStyle and indentation issues
 - last but not least, get rid of the following CONFIG_MODULE=n warning:

	drivers/net/arcnet/capmode.c:52: warning: ‘capmode_proto’ defined but not used

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: David S. Miller <davem@davemloft.net>