net/hyperv: Add support for jumbo frame up to 64KB

Allow the user set the MTU up to 65536 for Linux guests running on
Hyper-V 2008 R2 or later.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>