Fix VPP sends ARP requests for unknown destinations TC destination MAC address

-JIRA: CSIT-142
The ICMP packet was send to wrong destination.
Don't use resolve-attemts in add route.
Fix testcase.
Add testcase Sends ARP to GW with EXPECTED_FAILING.
Variable naming fix.
Documentation update.

Change-Id: I71a7a274c154c525b176c87884d089155d7ae61b
Signed-off-by: Matej Klotton <mklotton@cisco.com>