jvpp-benchmark: add option to select interface mode

jvpp-benchmark: add option to select interface mode

Changes:
- use loopback interface instead of local0,
- if L3 (default) mode is selected, assing IP to the loop0 interface,
- if L2 mode is selected, create bridge domain and assing loop0 the BD.

To test interface in L2 mode, use:

sudo java -jar ./target/jvpp-benchmark-exec.jar -p mode=L2

Change-Id: I8450d42fe0d164c6dbedf1dacf1444a25d9932b8
Signed-off-by: Marek Gradzki <[email protected]>