The copying of the first segment copied too small amount of data.
The copying of the second and subsequent segments used the wrong
data offset - for the case of GSO enabled it starts from 12 bytes
earlier.
Change-Id: I3adc532c175babc1ca1e121c7e12e6cafbdb9974
Type: fix
Ticket: VPP-1700 Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>