firewire: core: fix fw_send_request kerneldoc comment

The present inline documentation of the fw_send_request() in-kernel API
refers to userland code that is not applicable to kernel drivers at all.

Reported-by: Ben Gamari <bgamari.foss@gmail.com>

While we are at fixing the whole documentation of fw_send_request(),
also improve the rest of firewire-core's kerneldoc comments:
  - Add a bit of text concerning fw_run_transaction()'s call parameters.
  - Append () to function names and tab-align parameter descriptions as
    suggested by the example in Documentation/kernel-doc-nano-HOWTO.txt.
  - Remove kerneldoc markers from comments on static functions.
  - Remove outdated parameter descriptions at build_tree().

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>