dracut-module-setup.sh: skip installing driver for the loopback interface

Resolves: bz1958587
Upstream: Fedora
Conflict: None

commit 3b22cce1cb
Author: Coiby Xu <coxu@redhat.com>
Date:   Wed Dec 14 10:12:17 2022 +0800

    dracut-module-setup.sh: skip installing driver for the loopback
    interface

    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2151500

    Currently, kdump initrd fails to be built when dumping vmcore to
    localhost via ssh or nfs,

      kdumpctl[3331]: Cannot get driver information: Operation not supported
      kdumpctl[1991]: dracut: Failed to get the driver of lo
      dracut[2020]: Failed to get the driver of lo
      kdumpctl[1775]: kdump: mkdumprd: failed to make kdump initrd
      kdumpctl[1775]: kdump: Starting kdump: [FAILED]
      systemd[1]: kdump.service: Main process exited, code=exited, status=1/FAILURE
      systemd[1]: kdump.service: Failed with result 'exit-code'.
      systemd[1]: Failed to start Crash recovery kernel arming.
      systemd[1]: kdump.service: Consumed 1.710s CPU time.

    This is because the loopback interface is used for transferring vmcore and
    ethtool can't get the driver of the loopback interface. In fact, once
    COFNIG_NET is enabled, the loopback device is enabled and there is no driver
    for the loopback device. So skip installing driver for the loopback device.
    The loopback interface is implemented in linux/drivers/net/loopback.c
    and always has the name "lo". So we can safely tell if a network
    interface is the loopback interface by its name.

    Fixes: a65dde2d ("Reduce kdump memory consumption by only installing needed NIC drivers")
    Reported-by: Martin Pitt <mpitt@redhat.com>
    Reported-by: Rich Megginson <rmeggins@redhat.com>
    Reviewed-by: Lichen Liu <lichliu@redhat.com>
    Reviewed-by: Philipp Rudo <prudo@redhat.com>
    Signed-off-by: Coiby Xu <coxu@redhat.com>

Signed-off-by: Coiby Xu <coxu@redhat.com>

dracut-module-setup.sh

@@ -357,6 +357,7 @@ kdump_install_nic_driver() {
     _drivers=()
 
     for _netif in $1; do
+        [[ $_netif == lo ]] && continue
         _driver=$(_get_nic_driver "$_netif")
         if [[ -z $_driver ]]; then
             derror "Failed to get the driver of $_netif"
@@ -374,6 +375,7 @@ kdump_install_nic_driver() {
         _drivers+=("$_driver")
     done
 
+    [[ -n ${_drivers[*]} ]] || return
     instmods "${_drivers[@]}"
 }