BUG/MEDIUM: stconn: also consider SE_FL_EOI to switch to SE_FL_ERROR

BUG/MEDIUM: stconn: also consider SE_FL_EOI to switch to SE_FL_ERROR

In se_fl_set_error() we used to switch to SE_FL_ERROR only when there
is already SE_FL_EOS indicating that the read side is closed. But that
is not sufficient, we need to consider all cases where no more reads
will be performed on the connection, and as such also include SE_FL_EOI.

Without this, some aborted connections during a transfer sometimes only
stop after the timeout, because the ERR_PENDING is never promoted to
ERROR.

This must be backported to 2.7 and requires previous patch "CLEANUP:
stconn: always use se_fl_set_error() to set the pending error".