ovs-dpctl-top: in_port field is now the default view

This facilitates adding filtering since limiting output based on the in_port
is a natural first step.

Script mode was not changed allowing output to be piped through grep to
filter content.

Signed-off-by: Mark Hamilton <mhamilton@nicira.com>
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>