Changes

pySim/ts_51_011: Properly re-compute ScAddr length

EF.SMSP contains up to two addresses: Both are stored in a fixed-length
field of 12 octets.  However, the actually used size depends on the
number of digits in the respective number.  Let's compute that length
field properly

Change-Id: Idef54a3545d1a5367a1efa2f0a6f7f0c1f860105