FreeBSD: Provide correct file generation number

va_seq was actually a thin veil over va_gen, so z_gen is a more
appropriate value than z_seq to populate the field with.

Drop the unnecessary compat obfuscation and provide the correct
file generation number.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Ryan Moeller <freqlabs@freebsd.org>
Closes openzfs#12851

include/os/freebsd/spl/sys/vnode.h

@@ -132,7 +132,6 @@ vn_flush_cached_data(vnode_t *vp, boolean_t sync)
 /* TODO: This field needs conversion! */
 #define	va_nblocks	va_bytes
 #define	va_blksize	va_blocksize
-#define	va_seq		va_gen
 
 #define	MAXOFFSET_T	OFF_MAX
 #define	EXCL		0

module/os/freebsd/zfs/zfs_ctldir.c

@@ -496,7 +496,7 @@ zfsctl_common_getattr(vnode_t *vp, vattr_t *vap)
 	 */
 	vap->va_blksize = 0;
 	vap->va_nblocks = 0;
-	vap->va_seq = 0;
+	vap->va_gen = 0;
 	vn_fsid(vp, vap);
 	vap->va_mode = zfsctl_ctldir_mode;
 	vap->va_type = VDIR;

module/os/freebsd/zfs/zfs_vnops_os.c

@@ -2065,7 +2065,7 @@ zfs_getattr(vnode_t *vp, vattr_t *vap, int flags, cred_t *cr)
 	vap->va_size = zp->z_size;
 	if (vp->v_type == VBLK || vp->v_type == VCHR)
 		vap->va_rdev = zfs_cmpldev(rdev);
-	vap->va_seq = zp->z_seq;
+	vap->va_gen = zp->z_gen;
 	vap->va_flags = 0;	/* FreeBSD: Reset chflags(2) flags. */
 	vap->va_filerev = zp->z_seq;