int MLNewPacket(MLINK link) skips to the end of the current packet on link.
MLNewPacket() works even if the head of the current top-level expression is not a standard packet type.
MLNewPacket() does nothing if you are already at the end of a packet.
See The Mathematica Book: Section 2.12.13 and Section 2.12.14.
See also: MLNextPacket.