WITH_OFED build option: fix

Userspace has OFED build enabled for quite some time, but kernel modules
were not. This is useless config because any userspace IB code requires
kernel support. So enable modules build by default.

Move WITH_OFED to WITHOUT_OFED since defaults are now enabled.

Reviewed by: emaste, hselasky, kevans
MFC after: 3 days
Sponsored by: NVidia Networking / Mellanox Technologies
Differential Revision: https://reviews.freebsd.org/D28460