net/lwip: delete the useless member of the structure
net/lwip: delete the useless member of the structure

This patch delete the member stale_time as it is no use.

Change-Id: I51eff6f4abff1c88faaca1666cbd73a6be8d47d9
Signed-off-by: jisuu.kim <800dec47d2987cee7cc3d7aee71bc11b56f5042e@samsung.com>

JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT,JunhwanPark/TizenRT