kernel - Do not invalidate the vnode+children in the NFS core on ESTALE

* When NFS encounters ESTALE it would try to invalidate the related
  namecache topology in the core socket code, requiring an exclusive
  lock on related namecache entries.  This is not compatible with
  shared namecache locking because it can occur as part of any operation,
  even simple GETATTRs.

* Remove the invalidation for now.  The kernel already has a high-level
  solution in place for terminal nodes but we will also need one for
  traversals.
kernel: Port new device_pager interface from FreeBSD

Some parts implemented by François Tigeot and Matthew Dillon
kernel: add OBJT_MGTDEVICE in some more places
aio_return.3: The return type is ssize_t, not int.
kernel/bus: Remove NULL check after kmalloc with M_INTWAIT (w/o M_NULLOK).

Pointed-out-by: sephe
proto: Fix copy-n-paste error; PR_ASYNC_RCVD should be 0x0800.

It was defined to the same value as PR_ASYNC_SEND.  However, in the
current code base, it does not hurt, since only TCP has this flag set.
Merge branch 'mas1' into gsocdrm_github
Merge branch 'mas1' into gsocdrm_jfree