Aside from mutex, BSD always implements sx locks. They are a form of rwlock,
and according to BSD's sx.h, the differences from their own rwlock are an
implementation detail. Let's just use them as rwlocks for now.

The declarations are uglier than I wanted. But this file ends up being included
from c and cc code, and rwlock.h calls condvar.h inside - which is full of
sync_stub.h - and as a result condvar.h itself - are usually included in extern
"C" blocks. Because we are not expected to use sxlocks from C, it should be
fine.

As the comment states itself, mp_ncpus should be the number of CPUs
in the system, not the maximum number of CPUs. We can currently grab
that from the smp_processors variable.

I have audited the code for current users, though, and found two places
in which it is used as the maximum number of cpus. Those are changed to
MAXCPU

1. it is much cleaner that the header files perform extern "C" themselves,
   so they can be included both from C and C++ code.

2. when doing extern "C" from a C++ file then __cplusplus is also defined,
   and compilation can break in some situations.

3. as a bonus, this patch increase compilation time.

netport.h defines a log() macro, which is an unfortunate choice of name
because log is also a pretty-well-known mathematical function, and this

So rename this macro bsd_log(), and change the dozen files which used
log() to use bsd_log().

BSD and Solaris code likes to pass this identifier for the "kernel" process
to various thread creation routines.  Make our life simpler by providing it
and ignoring it.

the linux/musl definition is 2 bytes long instead of 1 byte as in
freebsd, this patch is fixing this issue which caused ifconfig to fail

Add includes where needed, remove duplicate definitions

This isn't actually a BSD native API as FreeBSD uses a per-cpu variable
to store cpuids, but rather a replacement we can use.

This flag implies the created thread is not started, but we currently
always start it. In addition the thread_lock/sched_add/thread_unlock
mess the BSD code usually does is something we'd rather avoid for now.

Various bits of BSD and Solaris code need to know the supported number
of CPUs.

This makes porting BSD and Solaris derived code a lot easier.

Note that I had to rename __unused to __unused2 as it conflicts with
various Linux headers.

We leave out the taskqueues running in software interrupts (OSv doesn't have
this concept and most likely never will), as well as those having timeouts
(we can add those once needed)

kthread are implemented on top of pthreads for now as they give us
a thread identifier easily usable from C code.

these are used by TCP.