setup route expiration in kernel if supported

setup route expiration in kernel if supported

kernel >= 4.5 (with commit https://github.com/torvalds/linux/commit/32bc201e1974976b7d3fea9a9b17bb7392ca6394) supports
RTA_EXPIRES netlink attribute to set router lifetime. This simply detect
the kernel version (>=4.5) and set the lifetime properly, fallback to
expiring route in userspace for kernel that doesnt support it.

Signed-off-by: Daniel Dao <dqminh89@gmail.com>