netdev-afxdp: Update memory locking limits unconditionally.

Any type of AF_XDP socket in all modes implies creation of BPF map of
type BPF_MAP_TYPE_XSKMAP.  This leads to BPF_MAP_CREATE syscall and
subsequently 'xsk_map_alloc()' function that will charge required
memory from the memlock limit and fail with EPERM if we're trying
to allocate more.

On my system with 64K bytes of max locked memory by default, OVS
frequently starts to fail after addition of 3rd afxdp port in SKB
mode:

  netdev_afxdp|ERR|xsk_socket__create failed (Operation not permitted)
                   mode: SKB qid: 0

Fixes: 0de1b42 ("netdev-afxdp: add new netdev type for AF_XDP.")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: William Tu <u9012063@gmail.com>

lib/netdev-afxdp.c

@@ -525,19 +525,12 @@ netdev_afxdp_reconfigure(struct netdev *netdev)
     netdev->n_rxq = dev->requested_n_rxq;
     netdev->n_txq = netdev->n_rxq;
 
-    if (dev->requested_xdpmode == XDP_ZEROCOPY) {
-        dev->xdpmode = XDP_ZEROCOPY;
-        VLOG_INFO("AF_XDP device %s in DRV mode.", netdev_get_name(netdev));
-        if (setrlimit(RLIMIT_MEMLOCK, &r)) {
-            VLOG_ERR("ERROR: setrlimit(RLIMIT_MEMLOCK): %s",
-                      ovs_strerror(errno));
-        }
-    } else {
-        dev->xdpmode = XDP_COPY;
-        VLOG_INFO("AF_XDP device %s in SKB mode.", netdev_get_name(netdev));
-        /* TODO: set rlimit back to previous value
-         * when no device is in DRV mode.
-         */
+    dev->xdpmode = dev->requested_xdpmode;
+    VLOG_INFO("%s: Setting XDP mode to %s.", netdev_get_name(netdev),
+              dev->xdpmode == XDP_ZEROCOPY ? "DRV" : "SKB");
+
+    if (setrlimit(RLIMIT_MEMLOCK, &r)) {
+        VLOG_ERR("setrlimit(RLIMIT_MEMLOCK) failed: %s", ovs_strerror(errno));
     }
 
     err = xsk_configure_all(netdev);