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
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