tests/netgraph: Inital framework for testing libnetgraph

Provide a framework of functions to test various netgraph modules.
Tests contain:
- creating, renaming, and destroying nodes
- connecting and removing hooks
- sending and receiving data
- sending ASCII messages and receiving binary responses
- errors can be passed for indiviual inspection or fail the test

Reviewed by: kp
Differential Revision: https://reviews.freebsd.org/D30629
Differential Revision: https://reviews.freebsd.org/D30657
Differential Revision: https://reviews.freebsd.org/D30671
Differential Revision: https://reviews.freebsd.org/D30699

(cherry picked from commit 24ea1dbf257aa6757f469bcd859f90e9ad851e59)
(cherry picked from commit 09307dbfb888a98232096c751a96ecb3344aa77c)
(cherry picked from commit 9021c46603bf29b9700f24b8dce8796b434d7c8f)
(cherry picked from commit 5554abd9cc9702af30af90925b33c5efff4e7d88)

Also contains some fixups:
- indent all files correctly
- finish factoring out
- remove debugging code
- check for renaming issues reported in PR241954

PR: 241954
Differential Revision: https://reviews.freebsd.org/D30692
Differential Revision: https://reviews.freebsd.org/D30714
Differential Revision: https://reviews.freebsd.org/D30713

(cherry picked from commit a664ade93972ce617f0888ff79e715dff9cf0f87)
(cherry picked from commit 0afa9be03937d60cb5aeba64c81e3e2165bd3737)
(cherry picked from commit 43e4821315c31db067e23564b9bfafb519e77b2b)

Git Hash: 4a0c1d0543afd83156b50b3f9b74c79e74cf526f
Git Author: donner@FreeBSD.org