Add zfs_disable_dup_eviction module option

Commit 1eb5bfa introduced a new zfs_disable_dup_eviction tunable.
It should have been made available as a module option in the
original patch but was overlooked.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/zfs/arc.c

@@ -5042,6 +5042,9 @@ MODULE_PARM_DESC(zfs_arc_shrink_shift, "log2(fraction of arc to reclaim)");
 module_param(zfs_arc_p_min_shift, int, 0444);
 MODULE_PARM_DESC(zfs_arc_p_min_shift, "arc_c shift to calc min/max arc_p");
 
+module_param(zfs_disable_dup_eviction, int, 0644);
+MODULE_PARM_DESC(zfs_disable_dup_eviction, "disable duplicate buffer eviction");
+
 module_param(l2arc_write_max, ulong, 0444);
 MODULE_PARM_DESC(l2arc_write_max, "Max write bytes per interval");