Build GENERIC with RACCT/RCTL support by default. Note that it still
needs to be enabled by adding "kern.racct.enable=1" to /boot/loader.conf.

Differential Revision: https://reviews.freebsd.org/D2407
Reviewed by: emaste@, wblock@
MFC after: 1 month
Relnotes: yes
Sponsored by: The FreeBSD Foundation