Add ${LIBC} to DPADD to fix "make checkdpadd"

Phabric: D632
Approved by: jmmv (mentor)
MFC after: 2 weeks
Replace dev_clone with cdevpriv(9) KPI in audit_pipe code.
This is (yet another) step towards the removal of device
cloning from our kernel.

CR:	https://reviews.freebsd.org/D441
Reviewed by:	kib, rwatson
Tested by:	pho
Bump the default size of cpuset_t masks in userland from 128 bits to 256.

This should not be an ABI change since the various public APIs that use
cpusets all include an explicit size parameter in addition to the cpuset
parameter.

MFC after:	1 week
Bump MAXCPU on amd64 from 64 to 256.  In practice APIC only permits 255
CPUs (IDs 0 through 254).  Getting above that limit requires x2APIC.

MFC after:	1 month
Fix build of si(4) and enable it in LINT on amd64 and i386.
Unexpand TAILQ_FOREACH().
Add kernel modules for si(4), wds(4), and wl(4).