J1939 with mixed 29/11 bit ID fails

[hacklint]

Description

J1939 requires 29-bit CAN identifiers, but it still should allow traffic on same bus with 11-bit IDs.
#997 contains a change that writes a warning instead
of throwing an exception if there is a .dbc file containing mixed 29/11 bit IDs. A modified version of
the CSS demo J1939 .dbc file is provided there as test data.