test: Add tests for passt in vhost-user mode

Run functional and performance tests for vhost-user mode as well. For
functional tests, we add passt_vu and passt_vu_in_ns as symbolic links
to their non-vhost-user counterparts, as no differences are intended
but we want to distinguish them in test logs.

For performance tests, instead, we add separate perf/passt_vu_tcp and
perf/passt_vu_udp files, as we need longer test duration, as well as
higher UDP sending bandwidths and larger TCP windows, to actually get
the highest throughput vhost-user mode offers.

For valgrind tests, vhost-user mode needs two extra system calls:
statx and readlink. Add them as EXTRA_SYSCALLS for the valgrind
target.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

test/lib/setup_ugly

@@ -33,7 +33,7 @@ setup_memory() {
 
 	pane_or_context_run guest 'qemu-system-$(uname -m)'		   \
 		' -machine accel=kvm'                                      \
-		' -m '${VMEM}' -cpu host -smp '${VCPUS}                    \
+		' -m '$((${MEM_KIB} / 1024 / 4))' -cpu host -smp '${VCPUS}                    \
 		' -kernel ' "/boot/vmlinuz-$(uname -r)"			   \
 		' -initrd '${INITRAMFS_MEM}' -nographic -serial stdio'	   \
 		' -nodefaults'						   \