Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

/* -> /*- for license, minor formatting changes

Remove advertising clause from University of California Regent's license,
per letter dated July 22, 1999.

Approved by: core

Move the typedef for size_t into _iovec.h, so that size_t is available
for struct iovec.

It is bad style to define the same structure in multiple header
files which might be included together.

Things like debuggers and lint-like programs get their knickers in
a twist (rightly so one might add) when they find different locations
for the same named struct depending on which .h file were included
first.

This is a stellar example of Very Bad Thinking on the part of the
standards dudes who wrote that both sys/uio.h and sys/socket.h
should define struct iovec the same way.

Fix this by putting struct iovec into its own miniature sys/_iovec.h
file and #include that from sys/socket.h and sys/uio.h.

Sensible people could just put iovec into sys/_types.h but there
is probably some standard or other which will be violated if we
did something that horrible.