fix: Fix a bug in --bidir option processing (#903)

If --bidir option was passed before --client option on command line,
the latter would override ipt->mode parameter of the test back to SENDER
or RECEIVER making the test hang during execution.

Fix this by checking if ipt->bidirectional was set to true in
iperf_set_test_role() function.

src/iperf_api.c

@@ -470,7 +470,9 @@ iperf_set_test_role(struct iperf_test *ipt, char role)
 {
     ipt->role = role;
     if (!ipt->reverse) {
-        if (role == 'c')
+        if (ipt->bidirectional)
+            ipt->mode = BIDIRECTIONAL;
+        else if (role == 'c')
             ipt->mode = SENDER;
         else if (role == 's')
             ipt->mode = RECEIVER;