tipc: rename dbg.[ch] to log.[ch]

As the first step in removing obsolete debugging code from TIPC the
files that implement TIPC's non-debug-related log buffer subsystem
are renamed to better reflect their true nature.

Signed-off-by: Allan Stephens <Allan.Stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>