Documentation: expand isdn/INTERFACE.CAPI document
Documentation: expand isdn/INTERFACE.CAPI document

- Note that send_message() may be called in interrupt context.
- Describe the storage of CAPI messages and payload data in SKBs.
- Add more details to the description of the _cmsg structure.
- Describe kernelcapi debugging output.

Impact: documentation
Signed-off-by: Tilman Schmidt <dc8b785d67b4628425f4b275427621124af5d812@imap.cc>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas