fix: Use the pcnet ethernet device for FreeDOS

FreeDOS does ship the Crynwr packet driver package, which does contain an
RTL8139 driver. However, you have to install the package after installing
FreeDOS, even if you performed a full install. It also seems to lock up for
me when attempting to load it.

The PCNet packet driver on the other hand, is installed with a full FreeDOS
install, is open source, and does work, at least for me.

quickemu

@@ -746,6 +746,11 @@ function configure_os_quirks() {
         NET_DEVICE="rtl8139"
     fi
 
+    if [ "${guest_os}" == "freedos" ]; then
+        NET_DEVICE="pcnet"
+    fi
+
+
     if [ "${guest_os}" == "freebsd" ] || [ "${guest_os}" == "ghostbsd" ]; then
         mouse="usb"
     fi