value-pairs: the DATE should always contain the stamp time

Formerly it contained sometimes the stamp time and sometimes the
received time. From now it will always contain the stamp time.

Signed-off-by: Daniel Gados <gdani@balabit.hu>
value-pairs: adding sdata to the syslog-proto (RFC5424) scope

Signed-off-by: Daniel Gados <gdani@balabit.hu>