Fix memory leak of ConnectivityManager

The instance of ConnectivityManager is static, and so its inner class
should be static to avoid the memory leak. Otherwise, the inner class
will get the reference to the mContext.

Bug:248184860

Signed-off-by: zhujiatai <zhujiatai@xiaomi.com>
Change-Id: I2c755f04a689f3e9e5f829d9be48765816257366