Reorder sysctls for spa.c global tunables; add sysctl for ccw_retry_interval.

MFC after:	1 month
Sponsored by:	Spectra Logic


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271785 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f