Windows: test for and react to SMB Extended Session Timeout support

Windows: test for and react to SMB Extended Session Timeout support

SMB Extended Session Timeout Support is available only on
Windows systems with specific versions of the mrxsmb.sys driver.
Add a test for those driver versions.  If a supporting version
is present use the extended session timeout value instead of the
standard timeout value for the redirector timeout.  Adjust the
rx hard, conn, and idle timeouts accordingly.

The SMB module will define the ExtendedSessTimeout registry
value if it does not exist.  We rely on the fact that this is
done after the rx timeout values are calculated.  The mrxsmb
driver only reads the value at boot.

LICENSE MIT

Reviewed-on: http://gerrit.openafs.org/248
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Asanka Herath <asanka@secure-endpoints.com>
Tested-by: Asanka Herath <asanka@secure-endpoints.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>