syscall: provide and use ioctlPtr for all BSD platforms

syscall: provide and use ioctlPtr for all BSD platforms

Provide ioctlPtr for all BSD platforms, then use this for BPF.
This reduces darwin specific code, as well as avoiding the use of
an indirect system call on OpenBSD.

Updates #63900

Change-Id: I81f3e74a3149150abe972f106903310e3cf26929
Reviewed-on: https://go-review.googlesource.com/c/go/+/540019
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: Josh Rickmar <jrick@zettaport.com>