transp_v6.h: style neatening

Use a more current code style.

Remove extern from function prototypes.
Align function arguments and reflow to 80 cols.
Use network comment styles.

Signed-off-by: Joe Perches <joe@perches.com>
cc: Lorenzo Colitti <lorenzo@google.com>,
Signed-off-by: David S. Miller <davem@davemloft.net>