net: pkt: Restore pkt cursor after cloning

net_pkt_clone() initializes the original packet cursor
and clone the packet. But it doesn't restore the cursor
back to original position.

Issue noticed when mDNS resolving fails when mdns responder
is also enabled.

net_conn_input(), in case of multicast packet, connection
handler clone the packet and deliver to matching handler.

Example case: dns_resolver and mdns_responder both register
handlers for 5353 port. After first clone original packet
cursor moved back to starting position. But first cloned
packet cursor is set properly. Second time cloning makes
cursor position to set to zero. Which makes second packet
handler header unpacking goes wrong.

Fixes #21970.

Signed-off-by: Ravi kumar Veeramally <ravikumar.veeramally@linux.intel.com>