proto_redistnum() uses strncmp() with invalid strlen assumption

[qlyoung]

lib/log.c:

int
proto_redistnum(int afi, const char *s)
{
  if (! s)
    return -1;

  if (afi == AFI_IP)
    {
      if (strncmp (s, "k", 1) == 0)
        return ZEBRA_ROUTE_KERNEL;
      else if (strncmp (s, "c", 1) == 0)
        return ZEBRA_ROUTE_CONNECT;
      else if (strncmp (s, "s", 1) == 0)
        return ZEBRA_ROUTE_STATIC;
      else if (strncmp (s, "r", 1) == 0)
        return ZEBRA_ROUTE_RIP;
      else if (strncmp (s, "o", 1) == 0)
        return ZEBRA_ROUTE_OSPF;
      else if (strncmp (s, "i", 1) == 0)
        return ZEBRA_ROUTE_ISIS;
      else if (strncmp (s, "bg", 2) == 0)
        return ZEBRA_ROUTE_BGP;
      else if (strncmp (s, "ta", 2) == 0)
        return ZEBRA_ROUTE_TABLE;
      else if (strncmp (s, "v", 1) == 0)
        return ZEBRA_ROUTE_VNC;
      else if (strncmp (s, "vd", 1) == 0)
        return ZEBRA_ROUTE_VNC_DIRECT;
    }
  if (afi == AFI_IP6)
    {
      if (strncmp (s, "k", 1) == 0)
        return ZEBRA_ROUTE_KERNEL;
      else if (strncmp (s, "c", 1) == 0)
        return ZEBRA_ROUTE_CONNECT;
      else if (strncmp (s, "s", 1) == 0)
        return ZEBRA_ROUTE_STATIC;
      else if (strncmp (s, "r", 1) == 0)
        return ZEBRA_ROUTE_RIPNG;
      else if (strncmp (s, "o", 1) == 0)
        return ZEBRA_ROUTE_OSPF6;
      else if (strncmp (s, "i", 1) == 0)
        return ZEBRA_ROUTE_ISIS;
      else if (strncmp (s, "bg", 2) == 0)
        return ZEBRA_ROUTE_BGP;
      else if (strncmp (s, "ta", 2) == 0)
        return ZEBRA_ROUTE_TABLE;
      else if (strncmp (s, "v", 1) == 0)
        return ZEBRA_ROUTE_VNC;
      else if (strncmp (s, "vd", 1) == 0)
        return ZEBRA_ROUTE_VNC_DIRECT;
    }
  return -1;
}

This is called in many locations with raw user's CLI input. In cases where the user matches one of the calling commands with a single letter for the protocol name, this function will fail.

Checking 1 or 2 letters is not consistent and breaks some CLI completions.

Broken out from #20.