Enable async use of libosmo-simtrace2

libosmo-simtrace2 traditionally had only supported blocking, synchronous
I/O, while remsim-client used asynchronous USB I/O.  Using async USB I/O
for IRQ + IN transfers while using blocking I/O for OUT transfers
doesn't seem to work reliably, so we have to switch OUT also to async.

Depends: simtrace2.git Ib8939bdb7f533cd20a34a30a97f12b782b9816c2
Change-Id: I18bf166a95bd4318d700b3e93401b2db5188acfc
diff --git a/src/client/user_simtrace2.c b/src/client/user_simtrace2.c
index c66f71e..5ce034d 100644
--- a/src/client/user_simtrace2.c
+++ b/src/client/user_simtrace2.c
@@ -412,6 +412,7 @@
 	if (cfg->usb.path)
 		osmo_strlcpy(ifm->path, cfg->usb.path, sizeof(ifm->path));
 	transp->udp_fd = -1;
+	transp->usb_async = true;
 	transp->usb_devh = osmo_libusb_open_claim_interface(NULL, NULL, ifm);
 	if (!transp->usb_devh) {
 		fprintf(stderr, "can't open USB device\n");