Fix mstp on bsd port (#1193)

* fix mstp on macos NS_PER_S is 1s and 0ns

* fix compile on freebsd

* port bsd: add compile warnings and comments

* port bsd: limit pthred prio to OS defined min/max value
e.g. FreeBSD min=0 max=31

* port bsd: fix clangformat

ports/bsd/readme.txt

@@ -1 +1,10 @@
 This is a port to MAC OS X or FreeBSD for testing.
+
+Install on FreeBSD 15
+sudo pkg install cmake git libdispatch
+git clone https://github.com/bacnet-stack/bacnet-stack.git
+cd bacnet-stack
+mkdir build
+cd build
+cmake ..
+make