Quick fix: fix receive and send callbacks in Zephyr IP adapter
Quick fix: fix receive and send callbacks in Zephyr IP adapter

This fix reads all fragments in a net_buf to retrieve the complete
payload in the receive callback. Previously it was reading only
the 1st fragment so things would break when it received a payload
of a size larger than the configured fragment size.

In addition, it fixes the oc_send_buffer() implementation to
send through the DTLS context for an outgoing encrypted packet.
Previously, it was sending all packets through the unsecured
UDP context.

Change-Id: Ib31ac92f892f2c843a9c10e23d85ef1f785c45c6
Signed-off-by: Kishen Maloor <c62ddea3cd661a9268bff15f07fc2229cdc9ac02@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18021

iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained