SelfLearnStrategy::InheritNpeExtra
fix fast ccnping causes abort in multi-thread

PROBLEM
ccnping with 1ms interval may cause assert failure in NamePrefixTable::SeekPit, or abort() in process_incoming_content2. These are not caused by memory full.
ROOT CAUSE
CcnbWireProtocol (stream mode) uses the same buffer for every read() syscall. CcnbMessage doesn't own the buffer. When a CcnbMessage is passed to core thread, a face thread may overwrite the buffer with a new message.
When the buffer happens to contain a different type of message, ccn_parse_interest or ccn_parse_ContentObject will fail.
FIX
If a message is returned based on a buffer, CcnbWireProtocol::State::GetReceive creates a new buffer and copy over any partial messages.
PERFORMANCE IMPACT
ccnping latency is increased from 3.0ms to 3.7ms.