Add additional bounds checks, ND_TTESTize existing ones.

Add additional bounds checks, ND_TTESTize existing ones.

Use ND_TTEST() and ND_TTEST2() for bounds checks.

Pass a pointer to the struct pkt_top to wb_dops, and calculate the
address of the first struct dophdr there.  Check each struct dophdr
before printing it.  Hopefully this will quiet a Coverity complaint.