gPTP - shorten timeouts for SYNC and ANNOUNCE receipt in slave mode
gPTP - simplify macros to add and subtract nanos from timestamp
gPTP - don't start sync timeout in slave mode until we recieve the first sync
gPTP - don't set AS capable flag until peer rate offset is set
gPTP - reject any PTP messages with incorrect transport specific field
gPTP - reject announce message if steps removed is too large
gPTP - set log mean message interval to 0x7F for outgoing PDelay response and PDelay response follow up messages
Merge pull request #37 from audioscience/asi-for-upstream-avb-next

Asi for upstream avb next