Fix build for FreeBSD 10.0

Move a rmlock.h inclusion up a bit so that the vm headers can get the
rmlock assertion (and other) macros they need.

The filedesc structure has been expanded on FreeBSD to support a
stronger capabilities system; getting to the actual file descriptor
requires another structure access.

limits.h and stdarg.h need sys/ and machine/ prefixes for inclusion in the
kernel on FreeBSD.  Unlike on master, we did not have extra -I arguments
to remove.

Catch up to VM layer changes.

This builds, but crashes at runtime due to some ABI incompatibilities
that appear in the rx event layer; those will be fixed in a separate patch.

Change-Id: Icc253b1e938a58a7ab8d1b789c82b9b940d263fd