Fix added proxy command when IPv6 is used

For explicit proxy commands (included with `-p "$P_PXY <args>` in the test
case), it's the test's writer responsibility to handle IPv6; only fix the
proxy command when we're auto-adding it.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>

tests/ssl-opt.sh

@@ -672,6 +672,10 @@ run_test() {
     # as it provides timing info that's useful to debug failures
     if [ -z "$PXY_CMD" ] && [ "$DTLS" -eq 1 ]; then
         PXY_CMD="$P_PXY"
+        case " $SRV_CMD " in
+            *' server_addr=::1 '*)
+                PXY_CMD="$PXY_CMD server_addr=::1 listen_addr=::1";;
+        esac
     fi
 
     # fix client port