papi: change default to use socket transport instead of shared memory transport
papi: change default to use socket transport instead of shared memory transport

In preparation for removing Python shared memory support, change the default to use sockets.
This may affect users of PAPI. E.g. if running against instances of VPP where
the API socket is in a different location or disabled.

Type: improvement
Signed-off-by: Ole Troan <aeed71d78dc09e4764ceac69b111eee9b50cfdd0@cisco.com>
Change-Id: I96308ed70b9ff314c9b487722174f5e4b14efdd2
Signed-off-by: Ole Troan <aeed71d78dc09e4764ceac69b111eee9b50cfdd0@cisco.com>

FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp