abis: skip e1_input nesting if empty

With this patch, we don't include e1_input if it's empty

[...]
    timeslot 7
     phys_chan_config TCH/F
     hopping enabled 0
e1_input <----------------- empty, it should not show up.
msc
[...]
1 file changed
tree: f0f1413fbb0d3a9bffc814b9b27ddebed4b37b46
  1. hlrsync/
  2. linux-kernel/
  3. openbsc/
  4. wireshark/
  5. README