Doing "smbclient -L //server_smb1 -U%" against a Samba server that supports both SMB1+SMB2 causes the error message:
smb1cli_req_writev_submit: called for dialect[SMB3_11] server[FILESERVERSMB1]
As we're issuing an SMB1 call on an SMB2-connection (the cli_cm_open("$IPC") call selects SMB2 by default).
We see this a lot in the provisioning code that uses smbclient -L to wait for the FILESERVERSMB1 server to start if you run an individual make test TESTS=.
Adds 2 regression tests showing the problem, then fixes them by setting the protocol to NT1 before calling the SMB1-only: list_servers(lp_workgroup()) code path.