The zfs_get_xattrdir() function is used to find the extended attribute

The zfs_get_xattrdir() function is used to find the extended attribute
directory for a znode.  When the directory already exists, it returns a
referenced but unlocked vnode.  When a directory does not yet exist, it
calls zfs_make_xattrdir() to create a new one.  zfs_make_xattrdir() returns
the vnode both referenced and and locked and zfs_get_xattrdir() was leaking
this vnode lock to its callers.  Fix this by dropping the vnode lock if
zfs_make_xattrdir() successfully creates a new extended attribute
directory.

Reviewed by:	pjd