StructInetDiagMsg#parse used absolute position to parse id and idiag_uid fields. This causes an issue when byte buffer contains multiple netlink messages and parsed netlink message starts from the middle of byte buffer. This CL fixes above issue and adds test for the case that single byte buffer contains multiple netlink messages. Test: atest NetworkStaticLibTests Change-Id: I771daf17b4a606915d5edefd9f0e90ef01abf168