datapath: Move generic tunnel functions to lisp module.

datapath: Move generic tunnel functions to lisp module.

Generic tunnel rcv and send function are only used by lisp tunneling
module, so It make sense to move them to lisp module.

CC: Lori Jakab <lojakab@cisco.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Lorand Jakab <lojakab@cisco.com>
Acked-by: Jesse Gross <jesse@nicira.com>