In the SMB3/SMB3.1.1 negotiate protocol request, we are supposed to
advertise CAP_MULTICHANNEL capability when establishing multiple
channels has been requested by the user doing the mount. See MS-SMB2
sections 2.2.3 and 3.2.5.2

Without setting it there is some risk that multichannel could fail
if the server interpreted the field strictly.
Reviewed-By: NTom Talpey <tom@talpey.com>
Reviewed-by: NShyam Prasad N <sprasad@microsoft.com>
Cc: <stable@vger.kernel.org> # v5.8+
Signed-off-by: NSteve French <stfrench@microsoft.com>