tipc: align usage of variable names and macros in socket

The practice of naming variables in TIPC is inconistent, sometimes
even within the same file.

In this commit we align variable names and declarations within
socket.c, and function and macro names within socket.h. We also
reduce the number of conversion macros to two, in order to make
usage less obsure.

These changes are purely cosmetic.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>