rearrange cpsw_start() a bit.
rearrange cpsw_start() a bit.

- cope with errors more consistently, which will avoid us leaking
  mbufs in failure paths.
- use m_defrag when we get EFBIG back from bus_dmamap_load_mbuf
  rather than printf and lose.
- shuffle some ops to be more like other drivers we have.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars