net: pkt: Clone cursor position in net_pkt_clone()

We need to make sure that net_pkt_clone() sets cursor correctly.
This cursor position is needed so that we can skip IP header
for incoming packet properly. Not all applications need to know
the cursor position of the cloned packet. Unfortunately we cannot
know that in advance so just set the cursor to correct position in
the cloned packet.

Fixes #19135

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>