Update tcpdump to 4.9.2.

[glebius]

Hi! I think phabrickator is useless for such kinds of things. Did you follow instructions in vendor/tcpdump/FreeBSD-upgrade?

[emaste]

@gordon and I discussed this at vBSDcon and he uploaded a diff between upstream tcpdump 4.9.2 and the merged changes, in D12405. Although it's missing context it's good to review to see if the expected FreeBSD changes are present.

[glebius]

D12405 looks good to me. Matches set of changed I had with 4.9.0. Is reduced actually, since tcpdump has incorporated some of our changes since.

Gordon, thanks a lot for handling that.