tipc: Cosmetic consolidation of internal message type definitions

Half of the #define entries in msg.h were down at the bottom
of the header, instead of up at the top before any of the static
inlines etc.   Relocate them up to the top, to be consistent with
the other normal linux header file layout conventions.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>