Fix unwind-info errors in our hand-written arm assembler code.

We have functions nested within functions, and places where we start a
function then never end it, we just jump to the middle of something else.
We tried to express this with nested ENTRY()/END() macros (which result
in .fnstart and .fnend directives), but it turns out there's no way to
express that nesting in ARM EHABI unwind info, and newer tools treat
multiple .fnstart directives without an intervening .fnend as an error.

These changes introduce two new macros, EENTRY() and EEND().  EENTRY()
creates a global label you can call/jump to just like ENTRY(), but it
doesn't emit a .fnstart.  EEND() is a no-op that just documents the
conceptual endpoint that matches up with the same-named EENTRY().

This is based on patches submitted by Stepan Dyatkovskiy, but I made some
changes and added the EEND() stuff, so blame any problems on me.

Submitted by:	Stepan Dyatkovskiy <stpworld@narod.ru>
Fix byte ordering in default RSS key.

The rss_key[] array in netinet/in_rss.c has the bytes in incorrect
order. This results in the RSS test vectors in the Microsft RSS spec
and Intel NIC specs giving incorrect results, and making it difficult
to verify correct hash operation when RSS functionality is added to
new NICs.

CR:		https://phabric.freebsd.org/D516
Reviewed by:	adrian