netinet6: allow binding a raw socket to an anycast address

Raw sockets have a separate check for this in rip6_bind() that was
missed in the previous change. This fixes e.g. 'ping -S' using an
anycast address.

Fixes: ca4b046105f6 ("netinet6: allow binding to anycast addresses")
Reviewed by: tuexen, kevans, des (previous version)
Approved by: kevans (mentor)
Differential Revision: https://reviews.freebsd.org/D50438