Rx: raise rx_minPeerTimeout to 20ms

Rx: raise rx_minPeerTimeout to 20ms

At 2ms it is possible for the packet we are sending to be resent
just about immediately as the retryTime computation occurs before
the send takes place and not afterwards.  If the network send blocks,
the retryTime may have already expired.

We do not want rx_minPeerTimeout to be too large though because the
value will end up being used as the backoff time period when the
actual RTT for the connection is less than the rx_minPeerTimeout
value.  Extensive testing shows 20ms to be an adequate compromise
that avoids the vast majority of unnecessary resends without
unnecessarily slowing down the connection if a packet is in fact
lost.

Reviewed-on: http://gerrit.openafs.org/2881
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit b62cacf889a6a231a97951baad6594e4066880bd)
Change-Id: Ieb4d8126477f9c8b293b8690a2e7f206de7ea92d
Reviewed-on: http://gerrit.openafs.org/3042