zfs_vnops_os.c: Move a vput() to after zfs_setattr_dir()

[rmacklem]

Without this patch, the following crash can occur when a file system is configured with "xattr=dir".

VNASSERT failed: locked not true at /posix-acl/freebsd-rdma/sys/kern/vfs_subr.c:5786 (assert_vop_locked) 0xfffff8001cc29370: type VDIR state VSTATE_CONSTRUCTED op 0xffffffff82fb2158
usecount 0, writecount 0, refcount 0 seqc users 0 mountedhere 0
hold count flags ()
flags ()
lock type zfs: UNLOCKED
panic: zfs_dirent_lookup: vnode is not locked but should be cpuid = 3
time = 1770520763
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00914c8140 vpanic() at vpanic+0x136/frame 0xfffffe00914c8270
panic() at panic+0x43/frame 0xfffffe00914c82d0
assert_vop_locked() at assert_vop_locked+0x78/frame 0xfffffe00914c82f0 zfs_dirent_lookup() at zfs_dirent_lookup+0x41/frame 0xfffffe00914c8340 zfs_setattr_dir() at zfs_setattr_dir+0x123/frame 0xfffffe00914c84a0 zfs_setattr() at zfs_setattr+0x1389/frame 0xfffffe00914c89e0 zfs_freebsd_setattr() at zfs_freebsd_setattr+0x56b/frame 0xfffffe00914c8b80 VOP_SETATTR_APV() at VOP_SETATTR_APV+0x5d/frame 0xfffffe00914c8bb0 setfown() at setfown+0xb1/frame 0xfffffe00914c8cc0 kern_fchownat() at kern_fchownat+0x192/frame 0xfffffe00914c8de0

This patch fixes the problem by moving the vput() call for attrzp to after the zfs_setattr_dir() call that takes it as an argument.

This was tested on a FreeBSD system with/without the patch by running a little
program that does the following (the file system is configured xattr=dir and "foo"
has a named attribute associated with it.

fd = open("foo", O_RDONLY | O_NOFOLLOW | O_PATH, 0);
fchownat(fd, "", 1001, 1001, AT_EMPTY_PATH);

Without the patch the above syscalls cause the crash.
With the patch, the above syscalls perform correctly.

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• [x ] My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• [x ] I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• [x ] All commit messages are properly formatted and contain Signed-off-by.