s3-smbd provide struct smbd_server_connection * to conn_snum_used

s3-smbd provide struct smbd_server_connection * to conn_snum_used

This provides the 'sconn' parameter to this key functions, that
is currently duplicated in dummysmbd.c, which causes duplicate symbol
issues in the waf build.

This has natrually caused a number of consequential changes across the
codebase, includning not passing a messaging context into initial
reload_services():

This causes problems because the global smbd_server_connection isn't
yet set up, as there isn't a connection here, just the initial
process.

Andrew Bartlett