iproute2: drop libresolv

iproute2: drop libresolv

Hello!

While building the iproute package in Debian I get warnings from
package helpers like this:

dpkg-shlibdeps: warning: package could avoid a useless dependency if debian/iproute/sbin/tc debian/iproute/usr/bin/lnstat debian/iproute/bin/ip debian/iproute/bin/ss debian/iproute/sbin/bridge debian/iproute/sbin/rtmon were not linked against libresolv.so.2 (they use none of the library's symbols)

The -lresolv in ./Makefile seems to come from pre-historic times (before
iproute2 git history, possibly from libc5/pre-glibc days).
I couldn't find out if/why there was any reason for linking to libresolv.
Does anyone know if there are any valid reasons for keeping it still?

If not, I'd be happy to see it go.... while at it I also removed includes
of <resolv.h> which I also couldn't find any reason for, but this is
just an added bonus of the patch (and there are probably more unneeded
includes that could be dropped in the same sources).

Signed-off-by: Andreas Henriksson <andreas@fatal.se>