MFC 324049,324077

MFC 324049,324077

324049
    hyperv/hn: Fix UDP checksum offload issue in Azure.

    UDP checksum offload does not work in Azure if following conditions are
    met:
    - sizeof(IP hdr + UDP hdr + payload) > 1420.
    - IP_DF is not set in IP hdr

    Use software checksum for UDP datagrams falling into this category.

    Add two tunables to disable UDP/IPv4 and UDP/IPv6 checksum offload, in
    case something unexpected happened.

    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D12429

324077
    hyperv/hn: Unbreak i386 building.

    Reported by:    cy
    Sponsored by:   Microsoft

git-svn-id: svn://svn.freebsd.org/base/stable/10@324468 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f