sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

infiniband: Opt-in for net epoch

This is counterpart to e87c4940156c, which did the same for ethernet.

Suggested by: hselasky
Reviewed by: hselasky, kib
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D39405

ofed: Mechanically convert to IfAPI

Summary:
Because of the intricacies of this code it wasn't purely scripted, but
instead hand-mechanical.

Reviewed by: hselasky
Sponsored by: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D38560

Use __FBSDID() for RCS tags in ibcore.

MFC after: 1 week
Sponsored by: Mellanox Technologies

sys: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

- Merge in OFED 1.5.3 from projects/ofed/head