virtiofsd: Add an option to enable/disable security label

virtiofsd: Add an option to enable/disable security label

Provide an option "-o security_label/no_security_label" to enable/disable
security label functionality. By default these are turned off.

If enabled, server will indicate to client that it is capable of handling
one security label during file creation. Typically this is expected to
be a SELinux label. File server will set this label on the file. It will
try to set it atomically wherever possible. But its not possible in
all the cases.

Signed-off-by: Vivek Goyal <[email protected]>
Message-Id: <20220208204813[email protected]>
Reviewed-by: Dr. David Alan Gilbert <[email protected]>
Signed-off-by: Dr. David Alan Gilbert <[email protected]>