bsd-user: do_freebsd_sysctl helper for sysctl(2)

bsd-user: do_freebsd_sysctl helper for sysctl(2)

Implement the wrapper function for sysctl(2). This puts the oid
arguments into a standard form and calls the common
do_freebsd_sysctl_oid.

Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Co-Authored-by: Juergen Lock <nox@jelal.kn-bremen.de>
Signed-off-by: Juergen Lock <nox@jelal.kn-bremen.de>
Co-Authored-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Stacey Son <sson@FreeBSD.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>