Use tvtohz() to convert a socket buffer timeout to a tick value rather than using a home-rolled version.  The home-rolled version could result in shorter-than-requested sleeps.
Use tvtohz() to convert a socket buffer timeout to a tick value rather
than using a home-rolled version.  The home-rolled version could result
in shorter-than-requested sleeps.

Reported by:	Vitja Makarov <vitja.makarov@gmail.com>
MFC after:	2 weeks

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