scapy: Load default SCAPY protocols

scapy: Load default SCAPY protocols

After the fix of SCAPY library import, it was not possible to use
some of the network protocols by T-Rex. T-Rex 2.38 uses by default
SCAPY 2.3.1 for python3, but it overrides the default set of network
protocols loaded by layers/all.py. VSPERF makefile was modified to
restore original version of all.py from SCAPY 2.3.1 git repository.
Also examples of scapy usage were updated to generate correct traffic
with modified scapy version.

JIRA: VSPERF-566

Change-Id: Ib9ae3c572e693e86d30eb0467ab9c812fe8f335b
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: Sridhar Rao <sridhar.rao@spirent.com>