IB/hfi1: Fix output trace issues from 16B change

The 16B changes to the output side of the header trace introduced
two issues:

1. An uninitialized field "l4" for 9B packets

   This field needs to be given a value of 0 for 9B
   packets to insure a correct 9B trace.

   The fix adds a new define to insure that there is a dummy
   default for 9B packets to insure the correct string
   is decoded.

2. Use of entry vs. __entry in field references

Fixes: Commit 863cf89d

 ("IB/hfi1: Add 16B trace support")
Reported-by: Kaike Wan <kaike.wan@intel.com>
Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>