dracut-module-setup.sh: pass ip=either6 param for ipv6

Kdump always use _proto=dhcp for both ipv4 and ipv6.  But for ipv6
the dhcp address assignment is not like ipv4, there are different ways
for it, stateless and stateful, see below document:
https://fedoraproject.org/wiki/IPv6Guide

In case stateless, kernel can do the address assignment, dracut use
_proto=auto6;  for stateful case, dracut use _proto=dhcp6.
But it is hard to decide whether stateless or stateful takes effect,
hence, dracut introduces ip=either6 option, which can try both of these
method automatically for us. For detail, refer to dracut:
commit 67354ee 40network: introduce ip=either6 option

We do not see bug reports before because for the most auto6 cases
kernel assign ip address before dhclient, kdump just happened to work.

Signed-off-by: Pingfan Liu <piliu@redhat.com>

dracut-module-setup.sh

@@ -293,6 +293,8 @@ kdump_setup_netdev() {
     _static=$(kdump_static_ip $_netdev $_srcaddr)
     if [ -n "$_static" ]; then
         _proto=none
+    elif is_ipv6_address $_srcaddr; then
+        _proto=either6
     else
         _proto=dhcp
     fi

kexec-tools.spec

@@ -50,7 +50,7 @@ Requires(post): systemd-units
 Requires(preun): systemd-units
 Requires(postun): systemd-units
 Requires(pre): coreutils sed zlib 
-Requires: dracut >= 046-7
+Requires: dracut >= 047-34.git20180604
 Requires: dracut-network >= 044-117
 Requires: ethtool
 BuildRequires: zlib-devel zlib zlib-static elfutils-devel-static glib2-devel bzip2-devel ncurses-devel bison flex lzo-devel snappy-devel