Fix build for mips.XLP64 kernel, by re-ordering headers

Fix build for mips.XLP64 kernel, by re-ordering headers

The log for the failure contained errors like this:

| In file included from ${SRCTOP}/sys/mips/nlm/dev/net/xlpge.c:34:
| In file included from ${SRCTOP}/sys/sys/systm.h:44:
| In file included from ./machine/atomic.h:849:
| ${SRCTOP}/sys/sys/_atomic_subword.h:222:37: error: unknown type name 'u_long'; did you mean 'long'?
| atomic_testandset_acq_long(volatile u_long *p, u_int v)
|                                     ^~~~~~
|                                     long

And similar "unknown type name" errors for u_int, not recognizing bool as a type, etc.

This was caused by including <sys/param.h> too far down; move it up where it belongs.

While here, add a blank line after '__FBSDID()', in keeping with convention.

Reviewed by:	emaste
Sponsored by:	Panasas
Differential Revision:	https://reviews.freebsd.org/D24242