src/libudev/util.c: bring in line with upstream

To bring this in line with upstream, we had to add in env-util.c.
The approach we will take is to slim down upstream's "shared" code
so that it only contains functions and macros for what we need.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
src/libudev/socket-util.h: slim down

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>