MFC [Hyper-V]: r293719-r293722, r293869-r293871, r293873-r293875, r293877

r293719 hyperv/hn: Implement LRO
r293720 hyperv/hn: Implement SIOC[SG]IFMEDIA support
r293721 hyperv/hn: Avoid mbuf cluster allocation, if the packet is small.
r293722 hyperv/hn: Removed unused netvsc_init()
r293869 hyperv/hn: Unbreak LINT-NOIP
r293870 hyperv: use x86 generic code to do the hypervisor detection
r293871 hyperv: remove unused vmbus definitions
r293873 hyperv: implement an event timer
r293874 hyperv: add interrupt counters
r293875 hyperv: set receive buffer size according to NVSP protocol version
r293877 Unbreak make depend with sys/modules/hyperv/vmbus after r293870

Approved by: re (glebius), adrian (mentor)
Sponsored by: Microsoft OSTC