ixgbe: fix vector receive of chained mbuf

ixgbe: fix vector receive of chained mbuf

When the vector pmd was receiving a mix of packets of various sizes,
some of which were split across multiple mbufs, there was an issue
with reassembly of the jumbo frames. This was due to a skipped increment
when using "continue" in a while loop. Changing the loop to a "for"
loop fixes this problem, by ensuring the increment is always performed.

Reported-by: Prashant Upadhyaya <praupadhyaya@gmail.com>
Reported-by: Martin Weiser <martin.weiser@allegro-packets.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Martin Weiser <martin.weiser@allegro-packets.com>