Normalize COMPAT_43 syscall declarations.

Have ogetkerninfo, ogetpagesize, ogethostname, osethostname, and oaccept
declare o<foo>_args structs rather than non-compat ones. Due to a
failure to use NOARGS in most cases this adds only one new declaration.

No changes required in freebsd32 as only ogetpagesize() is implemented
and it has a 32-bit specific implementation.

Reviewed by: kib
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D15816