Add branch prediction to ZFS_ENTER and ZFS_VERIFY_ZP macros

They are expected to fail only in corner cases.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Macy <mmacy@FreeBSD.org>
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Closes #11153

include/os/linux/zfs/sys/zfs_znode_impl.h

@@ -80,7 +80,7 @@ extern "C" {
 #define	ZFS_ENTER_ERROR(zfsvfs, error)				\
 do {								\
 	rrm_enter_read(&(zfsvfs)->z_teardown_lock, FTAG);	\
-	if ((zfsvfs)->z_unmounted) {				\
+	if (unlikely((zfsvfs)->z_unmounted)) {			\
 		ZFS_EXIT(zfsvfs);				\
 		return (error);					\
 	}							\
@@ -103,7 +103,7 @@ do {								\
 /* Verifies the znode is valid. */
 #define	ZFS_VERIFY_ZP_ERROR(zp, error)				\
 do {								\
-	if ((zp)->z_sa_hdl == NULL) {				\
+	if (unlikely((zp)->z_sa_hdl == NULL)) {			\
 		ZFS_EXIT(ZTOZSB(zp));				\
 		return (error);					\
 	}							\