lib/tsocket: make use of TEVENT_FD_ERROR in tstream_bsd_fde_handler()

lib/tsocket: make use of TEVENT_FD_ERROR in tstream_bsd_fde_handler()

This makes the logic introduced to fix bug #15202 simpler.

While developing this I noticed that a lot of callers
rely on the fact that they can read the pending bytes out
of the recv queue before EOF is reported.

So I changed the code handle TEVENT_FD_ERROR together with
TEVENT_FD_READ in a way that keep the existing callers happy.

In the next step we'll add a way to let callers opt-in in order
to fail immediately if TEVENT_FD_ERROR appears (even if there
are pending bytes remaining in the recv queue).

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15202

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>