Linux 4.16 compat: inode_set_iversion()

A new interface was added to manipulate the version field of an
inode.  Add a inode_set_iversion() wrapper for older kernels and
use the new interface when available.

The i_version field was dropped from the trace point due to the
switch to an atomic64_t i_version type.

Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Chunwei Chen <david.chen@nutanix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #7148

module/zfs/zpl_super.c

@@ -36,7 +36,7 @@ zpl_inode_alloc(struct super_block *sb)
 	struct inode *ip;
 
 	VERIFY3S(zfs_inode_alloc(sb, &ip), ==, 0);
-	ip->i_version = 1;
+	inode_set_iversion(ip, 1);
 
 	return (ip);
 }