iputils: resolve musl compatibility

The new upstream is a fork of the original that consolidates other distro's
patches.  This fork resolves a series of musl build failures noted in the
autobuilder log.

http://autobuild.buildroot.net/results/12cb73f3def95efe706bcd957bc2c091e7931d5a/

  - Updated to github fork, selected merge from Nov 3 2015
    which provided musl fixes (last release was to old, 20150815)
  - Why the fork ? (http://www.spinics.net/lists/netdev/msg279881.html

)
  - Added missing dependencies for kernel capabilies lib
  - Accounted for new consolidated ping (ipv4/6)

Tested against a buildroot arm musl/glibc toolchains, as well as
autobuilder defconfig.

Signed-off-by: Matt Weber <matt@thewebers.ws>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>