[CIFS] Make socket retry timeouts consistent between blocking and nonblocking cases

We have used approximately 15 second timeouts on nonblocking sends in the past, and
also 15 second SMB timeout (waiting for server responses, for most request types).
Now that we can do blocking tcp sends,
make blocking send timeout approximately the same (15 seconds).

Signed-off-by: Steve French <sfrench@us.ibm.com>