Make sw_interface_dump more compatible with 2.2.0

Make sw_interface_dump more compatible with 2.2.0

+ As old PAPI clients are likely to put zero as the value
  for sw_if_index, the behavior should not perform
  index filtering at least when name filtering is enabled (valid).
+ interface.api version set to 2.3.0,
  as the new behavior is backward compatible
  (at least for PAPI with name filter enabled),
  but not forward compatible.
+ Minor whitespace cleanup.

Change-Id: I315a0eae4004f9d9b6c5f9ecf0f179e669729118
Signed-off-by: Vratko Polak <vrpolak@cisco.com>