When we want to run multiple instances of the card-emulator (e.g. for
multi-modem/multi-card versions of the hardware), the code shouldn't be
using any global variables but have them per-instance.
We now auto-discover the end-point addresses based on the interface
descriptor. The user can also use the new "--interface" command line
argument to set a non-zero intrerface. In combination, this should
enable support for the remote-sim functionality on the second UART
on OWHW.
