zebra: make routing socket debug user friendlier

zebra: make routing socket debug user friendlier

Implement a addrs RTA to string translator to provide more useful
debug output.

Example:

ifam_read_mesg: ifindex 2, ifname em1, ifam_addrs NETMASK,IFP,IFA
  ifam_flags 0x4, addr 2001:db8:1::1/64 broad (unspec) dst (unspec)
  gateway (unspec)

Instead of:

ifam_read_mesg: ifindex 2, ifname em1, ifam_addrs 0x34
  ifam_flags 0x4, addr 2001:db8:1::1/64 broad (unspec) dst (unspec)
  gateway (unspec)

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>