Determining capabilities of peer computer in samba4

[derrell at samba.org]

In samba4, how might one discover the capabilities of a peer, to select which
of the various "raw" functions to use?  For example, if I want to open a file,
is there a way to determine whether I should be using t2open, openold or openx
(a few of my choices in union smb_open)?  Similarly for other raw facilities
where multiple functions exist.  We clearly want to use the most "recent" or
complete function that the peer will accept, but it'd be nice not to have to
try them in descending order of preference if there's some better way to
figure out which should be used.

Derrell