bhyve: validate e82545 checksum offset field
Reported by: Mehdi Talbi, Synacktiv
(cherry picked from commit b0aa20bec5db244980a0248e24dd6b8e1e68c4d0)
(cherry picked from commit 53f72209479885dfa6a7e6ed68cbc82c68464f4b)
(cherry picked from commit 629df7c108abe26496c3a5c196cce79a47bc1f21)