Windows: Use interlocked ops for cm_conn flags

cm_conn flags can be modified by multiple threads.
Use interlocked operations for thread safety.

Change-Id: Iaaec54ca0962f8f78e1ddaee2c0a8a68041f5ed9
Reviewed-on: http://gerrit.openafs.org/9846
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: Introduce CM_CONN_FLAG_NEW

The new CM_CONN_FLAG_NEW flag is set on the cm_conn object whenever
a new rx_connection has been created.   The flag is cleared in cm_Analyze
if the call succeeded or if the error is one that is generated as a
result of communicating with the peer.  If no communication with the
peer has taken place the connection is considered "new".

For errors that would result in forcing a new connection, check whether
the existing connection is already "new".  This avoids an extra
RX_CALL_DEAD timeout period in the case where a "new" connection was
already in use.

Change-Id: If23a5f4b98e7599e4b4e62b474661e9d91aba81b
Reviewed-on: http://gerrit.openafs.org/9847
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>