Rx: Correct AFS_NT40_ENV rx_GetIFInfo max MTU assignments

Rx: Correct AFS_NT40_ENV rx_GetIFInfo max MTU assignments

On UNIX, the rx library values for rx_maxReceiveSize and
rx_MyMaxSendSize are sent by the cache manager directly.
In Windows, they are set by rx_GetIFInfo() which had two
errors.

(1) The comparison of rx_maxReceiveSize and maxsize were
    reversed which prevented rx_maxReceiveSize from ever
    being set to the interface MTU.

(2) rx_MyMaxSendSize was never assigned a value.

As a result, two problems occurred.

(1) The remote peer was never told about the local MTU.

(2) The local peer ignores the MTU.

From 1.3.60 to 1.5.33, OpenAFS for Windows installers
provided a registry default RxMaxMTU of 1260.  This caused
the cache manager to call rx_SetMaxMTU() which in turn set
both rx_maxReceiveSize and rx_MyMaxSendSize in effect
masking these errors.

Change-Id: Ib05927d7985052e233ff6f4bd170a939eb05c320
Reviewed-on: http://gerrit.openafs.org/1107
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>