net: use strnstr() for lwip_strnstr()

Using strstr() instead of strnstr() creates a security concern.

Fixes: 1c41a7afaa15 ("net: lwip: build lwIP")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
1 file changed