Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Move mostly useless examples binaries from OFED, as well as the Subnet
Manager, under the new option WITH_OFED_EXTRA, disabled by default.

Reviewed by: bdrewery, hselasky (previous version)
Sponsored by: Mellanox Technologies
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D16230

Rework ofed build.

Aligns the build with the FreeBSD traditional approach to not build in
contrib/, and to track inter-dependencies between libraries.

With help from: bdrewery
Reviewed by: bdrewery, hselasky
Sponsored by: Mellanox Technologies
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D15648