Fix a bug introdiced in r217548.  According to NS DP83815 data
sheet, RX filter should be disabled before programming.
Previously it was clearing wrong bits so RX filter was not
disabled in RX filter configuration.

Reported by:	brad@OpenBSD.org


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275816 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f