[paging] Move the paging state into struct gsm_bts

There is a 1:1 relationship between gsm_bts and the paging
operation. Move the paging state into the gsm_bts which is
simplfying the code a lot. This was hinted by LaF0rge.

(I'm not happy with the names of the structs)

tree: 5984ab62e5fcb3cccd4d68655f6d8377f139fe91
  1. tests/
  2. tools/
  3. AUTHORS
  4. configure.in
  5. COPYING
  6. Makefile.am
  7. README