utilities/ovs-ctl: Force removal of ip_gre/gre

On Linux kernels older than 4.16 the user cannot take advantage of
OVS ERSPAN features if the older ip_gre and gre kernel modules are
loaded.  In addition, the openvswitch kernel module will fail to
load because it cannot grab the IPPROTO_GRE inet protocol handler
since the gre kernel module has already taken it.

Update the force_reload_kmod() script function to force removal
of the ip_gre and gre built-in kernel modules so that the openvswitch
kernel module can load and provide support for ERSPAN.

Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

utilities/ovs-lib.in

@@ -622,6 +622,14 @@ force_reload_kmod () {
         action "Removing $vport module" rmmod $vport
     done
 
+    if test -e /sys/module/ip_gre; then
+        action "Forcing removal of ip_gre module" rmmod ip_gre
+    fi
+
+    if test -e /sys/module/gre; then
+        action "Forcing removal of gre module" rmmod gre
+    fi
+
     if test -e /sys/module/openvswitch; then
         action "Removing openvswitch module" rmmod openvswitch
     fi