Draft: Fix compatibility with Linux 6.3 and the other bugs I found

dahdi fails to build for Linux 6.3. While investigating this I found a lot of compiler warnings indicating other bugs, which I've also tried to fix:

• Update to follow kernel changes:
  • kernel 5.15 API change: use dev_addr_set()
  • kernel 5.16: Fix fallthrough warnings
  • kernel 6.3 API change: uevent takes const device pointer
• wcte1xxp: Fix setting linemode J1
• drivers: Fix array address test warnings
• Stop building dahdi_dummy module which does nothing
• wcte13xp, wcte43x: Fix cleanup bugs

Also restore debian/.gitignore which was lost in a source package import, and delete the unused patches.

This goes on top of !4 (merged).