s4:libcli/smb2: allow smb2_connect*() to fake session and tcon

s4:libcli/smb2: allow smb2_connect*() to fake session and tcon

For multichannel connection we want a way to have just a connection
with a negprot finished.

For now we just fake a tcon and session in order to avoid changes in the
caller. We can clean that up later if needed.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>