bhyve: Propagate errors from rfb_recv_* functions

Update rfb_recv_* functions to return -1 on failure and 0 on success.
Update rfb_handle to check these return values and drop the connection
if an error occurs.

Signed-off-by: Hayzam Sherif <hayzam@gmail.com>

Reviewed by: markj
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation