Fix some of the races (but probably not all of them) in the NFS server code.
nfssvc_nfsd(): change a splsoftclock()/spx() to mutex_enter/exit(&nfsd_lock)
(I guess it was forgotten when the nfsd code was made SMP safe)
m_freem(nd_nam) in nfsrv_slpderef() instead of nfsrv_zapsock() to
avoid possible use after free in nfssvc_nfsd()
Fix nfsrv_slpderef() to not release nfsd_lock before testing SLP_VALID
and reaquiring it just after. This could cause a use after free
of the slp if one thread is in nfsrv_slpderef() and the other one grabs
slp from nfssvc_sockpending and zap it.
615c2e4e8d