linux.core: Add network events and fields to the kernel layout

linux.core: Add network events and fields to the kernel layout

Event matching definitions can then make use of those events and fields

Change-Id: I0a71de243f74519241ebd2eebbb8ea5a7313bd35
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/77799
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Alexandre Montplaisir <alexmonthy@efficios.com>