bugfix: Ethernet type and vnf stop fixes

bugfix: Ethernet type and vnf stop fixes

Usage of ethernet type for IPv4 was harmonized, to use
0x0800 at all places. Together with this fix a bug during
VNF cleanup was removed - VNF started by TestSteps are
tested for validity before the call of their stop() method.
It avoid vsperf crash in case, that VNF was not properly
started.

JIRA: VSPERF-436

Change-Id: Ic1a36919f5c9d707aa0aad64b5d96a1214c56cb3
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Bill Michalowski <bmichalo@redhat.com>
Reviewed-by: Antonio Fischetti <antonio.fischetti@intel.com>
Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>