Initialize paddr to handle the case of zero size.

Reported and reviewed by:	Conrad Meyer <cemeyer@uw.edu>
MFC after:	1 week
Put the offset of the CRC32C in csum_data instead of 0.
The virtio driver needs the offset to be stored in csum_data,
like in the case for UDP and TCP.

The virtio problem was reported by
Niu Zhixiong <kaiaixi@gmail.com>, who helped in debugging
and testing the patch.

MFC after: 3 days
Since 32-bit if_baudrate isn't enough to describe a baud rate of a 10 Gbit
interface, in the r241616 a crutch was provided. It didn't work well, and
finally we decided that it is time to break ABI and simply make if_baudrate
a 64-bit value. Meanwhile, the entire struct if_data was reviewed.

o Remove the if_baudrate_pf crutch.

o Make all fields of struct if_data fixed machine independent size. The
  notion of data (packet counters, etc) are by no means MD. And it is a
  bug that on amd64 we've got a 64-bit counters, while on i386 32-bit,
  which at modern speeds overflow within a second.

  This also removes quite a lot of COMPAT_FREEBSD32 code.

o Give 16 bit for the ifi_datalen field. This field was provided to
  make future changes to if_data less ABI breaking. Unfortunately the
  8 bit size of it had effectively limited sizeof if_data to 256 bytes.

o Give 32 bits to ifi_mtu and ifi_metric.
o Give 64 bits to the rest of fields, since they are counters.

__FreeBSD_version bumped.

Discussed with:	emax
Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
Add hyperv manual pages provided by Microsoft, formatted
for FreeBSD standards.  Very little, if any, content was
modified.

These are not yet linked to the build.

Submitted by:	Abhishek Gupta (abgupta!microsoft dot com)
Sponsored by:	The FreeBSD Foundation
Connect the hyperv drivers to the build.

MFC after:	5 days
X-MFC-With:	r263105
Sponsored by:	The FreeBSD Foundation
To avoid missing a chance to cancel thread, call _pthread_testcancel at the
beginning of _sem_timedwait.

Submitted by:	Eric van Gyzen &lt; eric at vangyzen dot net &gt;
MFC after:	3 days