kdump-lib: check kdump service state when validating fadump load

Currently, kdumpctl status reports kdump as operational even when
the kdump service is in a failed state for fadump.

root> kdumpctl status
kdump: Dump mode is fadump
kdump: Kdump is operational

root> systemctl status kdump
× kdump.service - Crash recovery kernel arming
     Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled; preset: enabled)
     Active: failed (Result: exit-code) since Tue 2026-01-20 02:52:59 CST; 12s ago
<snip...>
cp: error writing '/boot/initramfs-6.12.0-180.el10.ppc64le.img.tmp': No space left on device
dracut[F]: Creation of /boot/initramfs-6.12.0-180.el10.ppc64le.img.tmp failed
<snip...>

This happens because the kernel registers fadump during early boot
[1]. Even if the kdump service later fails to start due to a failure
while updating the initrd with the fadump component,
/sys/kernel/fadump/registered still remains set to 1. As a result,
kdump is reported as operational, even though it is not.

Fix this by checking the kdump service state when validating the
fadump load.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=607451ce0aa9bdff590db4d087173edba6d7a29d

Reported-by: Shirisha G <shirisha@linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>

Author: sourabhjains

kdump-lib.sh

@@ -375,6 +375,7 @@ is_kernel_loaded()
 		;;
 	fadump)
 		_sysfs="$FADUMP_REGISTER_SYS_NODE"
+		systemctl is-active --quiet kdump.service || return 1
 		;;
 	*)
 		derror "Unknown dump mode '$_mode' provided"