[issue1872] nfs stall (fix pushed)

[Matthew Dillon]

::I reduced vfs.nfs.maxasyncbio to 16 (from default of 64),
::and haven't seen the 'Insufficient sendspace' since.
::
::NFS stall can still be experienced, if I do 'too many' things at once,
::e.g. doing `git status' with repo and checkout on NFS mounts while
::doing `make -j3 buildworld' did stall NFS.
::
::Forced core dump avail. on request.

    I have pushed a fix to 2.8 and master for UDP mounts sometimes
    losing track of rpc replies.  This only applies to UDP mounts.
    TCP mounts should not have had this issue.

    It is not 100% tested yet but I'd like to see if it solves the
    UDP NFS mount issue you are reporting.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>