hotfix: clear DCI padding bits

The problem is the following (as reported by an user):

"one UE is attached to OAI system. UE is near the antenna. Try to detach the UE and attach again. Repeat this procedure for 5-6 times. OAI system does not work and any the UE can not attach to this system. I use TEMS software and I can see MIB signaling on this UE but UE can not decode SIB1 and SIB2."

What happens is that the DCI for SIB1 and SIB2 is not cleared before use. That is the bits in the 'padding' field keep the values that were set before. If the structure has been used to transmit other DCIs (eg. for UEs) in the past, it may be reused with some of those bits set to 1. When receiving this DCI, the UE won't accept it because it gets some bits at 1 where it expects them to be 0.

The short-term/quick solution is to clear the 'padding' field. A better solution would be to rewrite this part of the code, which is way too complicated for what it does. But this takes too much time.

In dci.h the field 'dummy' of some structures was renamed to 'padding'. The fields 'padding32' and 'padding64' were also renamed to 'padding' for consistency.

Some structures (DCI2B_1_5MHz_TDD, DCI2B_10MHz_FDD, DCI2D_1_5MHz_FDD, DCI2D_5MHz_FDD, DCI2D_10MHz_FDD) had a 'padding' field at the end, which was renamed to 'padding0'. I don't know if this field should be here at all. To me this field looks very suspicious. When we test DCIs 2B and 2D we should be careful.