hyperv/hn: Use m_copydata for chimney sending.

[sepherosa_gmail.com]

Summary

While I'm here, move stack variables near their usage.

[sepherosa_gmail.com]

If no objection comes, it will be committed two days later

[howard0su_gmail.com]

sys/dev/hyperv/netvsc/hv_netvsc_drv_freebsd.c

947 ↗

(On Diff #12412)

why uint8*? the last parameter is caddr_t

m_copydata(const struct mbuf *mbuf, int offset, int len, caddr_t buf);

[sepherosa_gmail.com]

sys/dev/hyperv/netvsc/hv_netvsc_drv_freebsd.c

947 ↗

(On Diff #12412)

caddr_t is char *, I generally like to use uint8_t * for byte array, instead of char *. I don't think we have -Wpointer-sign in kernel compiling cc flags, so uint8_t * has same effect as char */caddr_t for m_copydata()

[delphij]

Looks good to me.