Switch to official tarballs. Simpler and faster.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Add missing includes to libbridge.h to define struct timeval and the
required u_int*_t types under musl.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

* update Makefile accoring to CONTRIBUTING.md, set maintainer
* fix file offset handling
* use https://git.kernel.org/pub/scm/linux/kernel/git/shemminger/bridge-utils.git for source code

Signed-off-by: Nikolay Martynov <mar.kolya@gmail.com>