s3: Add cli_smb()

s3: Add cli_smb()

This is a sync wrapper around cli_smb_send/cli_smb_recv. This is a hack to
speed up converting libsmb/ away from cli_send_smb/cli_receive_smb. Some
routines in libsmb/ are only called in one place in smbtorture for example,
where making it async right now is not worth it. With cli_smb_send/cli_smb_recv
in place, pushing the asynchronosity out one level is "just" boilerplate code
that is easy to do should it become necessary.