Set SMB2 as default highest allowed protocol

[0x6B386F]

Fixes #179

[mike42]

@1dal - thanks for writing this pull request.

I don't have a post-Windows 7 setup to test that this resolves #179, but the code's fine, and I'm planning to merge for the next release.

[boudafc]

Hello, I have made a test on Windows 10, it seems doesn't work:
Failed to print. Command "smbclient '//xxx.xxx.xxx.xxx/oxhoo_tp50' -c 'print -' -N -m SMB2" failed with exit code 1: WARNING: The "syslog" option is deprecatedNT_STATUS_ACCESS_DENIED opening remote file stdin-4423
I could not do more tests for now because it is on production computer but by removing "-m SMB2" it prints again.
However I could try to do more tests if you want.