ANDROID: add flags variable to nfs4_xattr_get_nfs4_user()

nfs4 just got xattr support, so add the required extra "flags" variable
as Android has an out-of-tree patch that adds this to all of these
callbacks.

Bug: 133515582
Bug: 136124883
Bug: 129319403
Cc: Mark Salyzyn <salyzyn@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I4260d16eb469047f62b37c8226c2c1c9cd04cf75