When VOP_SYMLINK fails, the value of *vpp is junk, so we must NULL out nd.ni_vp to prevent the resource cleanup code at the end of nfsrv_symlink from trying to vrele it. This fixes a "vrele: negative ref cnt" panic that can occur when a symlink is attempted on an NFS filesystem with no free space. Found locally, but the symptoms correspond to those in the PR referenced below.
When VOP_SYMLINK fails, the value of *vpp is junk, so we must NULL
out nd.ni_vp to prevent the resource cleanup code at the end of
nfsrv_symlink from trying to vrele it. This fixes a "vrele: negative
ref cnt" panic that can occur when a symlink is attempted on an NFS
filesystem with no free space. Found locally, but the symptoms
correspond to those in the PR referenced below.

PR:		kern/26878
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase