Improve coments on structures in trigger.c

Hi,

I found that comments in trigger.c describing fields of three different
structures in a comment block. I feel this is confusing because some
structure names are not explicitly mentioned there even though common field
names are used between structures. I've attached a patch to improve the comments
by splitting it to three blocks.

Regards,
Yugo Nagata

-- 
Yugo Nagata <nagata@sraoss.co.jp>