update arc_summary arcstat patch with new introduced values

update arc_summary arcstat patch with new introduced values

ZFS 2.2.4 added new kstats for speculative prefetch in:
026fe796465e3da7b27d06ef5338634ee6dd30d8

Adapt our patch introduced with ZFS 2.1 (for the then added MFU/MRU
stats), to also deal with the now introduced values not being present
(because an old kernel-module does not offer them).

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Reviewed-by: Max Carrara <m.carrara@proxmox.com>
Tested-by: Max Carrara <m.carrara@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>