correct pkthdr length calculation for ipv6 echo packets; after moving a packet header with M_MOVE_PKTHDR one should not reference the packet header in the original packet; in this case the code was assuming that m_adj would alter m_pkthdr.len which stopped happening because M_MOVE_PKTHDR removes the M_PKTHDR bit from m_flags
correct pkthdr length calculation for ipv6 echo packets; after moving a packet
header with M_MOVE_PKTHDR one should not reference the packet header in the
original packet; in this case the code was assuming that m_adj would alter
m_pkthdr.len which stopped happening because M_MOVE_PKTHDR removes the
M_PKTHDR bit from m_flags

Submitted by:	Bill Fenner <fenner@research.att.com>

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