The default for UDPLITE_RECV_CSCOV is zero. RFC 3828 recommend
that this means full checksum coverage for received packets.
If an application is willing to accept packets with partial
coverage, it is expected to use the socekt option and provice
the minimum coverage it accepts.

Reviewed by: kevlo
MFC after: 3 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272347 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f