odhcp6c: update to git HEAD version

c13b6a0 dhcpv6: fix white space error
e9d80cc dhcpv6: trigger restart of DHCPv6 state machine when not
		receiving statefull options
c7122ec update README
419fb63 dhcpv6: server unicast option support

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>