runs on boot and each time a vnet jail is created. Running cc_init() multiple
times results in a panic when attempting to initialise the cc_list lock again,
and so r215166 effectively broke the use of vnet jails.

Switch to using a SYSINIT to run cc_init() on boot. CC algorithm modules loaded
on boot register in the same SI_SUB_PROTO_IFATTACHDOMAIN category as is used in
this patch, so cc_init() is run at SI_ORDER_FIRST to ensure the framework is
initialised before module registration is attempted.

Sponsored by:	FreeBSD Foundation
Reported and tested by:	Mikolaj Golub <to.my.trociny at gmail com>
MFC after:	11 weeks
X-MFC with:	r215166