net: ptp: Add event generation and event handler for PTP Port

Introduction of PTP stack's core functions responsible for
event generation and handling of these events. Events are generated
base on timeouts and/or PTP messages received via BSD sockets
assigned to a specific PTP Port. These function will be used
in PTP thread.

Signed-off-by: Adam Wojasinski <awojasinski@baylibre.com>