NFS: Force the legacy idmapper to be single threaded
NFS: Force the legacy idmapper to be single threaded

It was initially coded under the assumption that there would only be one
request at a time, so use a lock to enforce this requirement..

Signed-off-by: Bryan Schumaker <8d60cd65e947920c1efaaf1b4ff723c7aa255e6d@netapp.com>
CC: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org [3.4+]
Signed-off-by: Trond Myklebust <6a1f9db795c9fc44be97d66ab114c53193bd3d13@netapp.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs