LL70: Use of the term "valid"

In looking over Issue LL70, I've come to the conclusion that the term
"valid" is used gratuitously in several places, and that in several
cases the term can be removed without doing damage.  If this is done,
I think that a normative reference to [DNAv4] will not be required.

Section 1.9:

"For these reasons, a host SHOULD NOT have both a valid routable address and a
Link-Local IPv4 address configured on the same interface."

I don't think the term "valid" is useful here.  If the routable address is
invalid then it should not be configured.  The term can be deleted
without changing the meaning.

"   A "valid routable address" is a routable address that passes the
   reachability test described in section 2 of "Detection of Network
   Attachment (DNA) in IPv4" [DNAv4]."

This definition belongs in the terminology section, not here and in any
case it differs from the definition used in [DNAv4].  Recommend adding the
following definition to Section 1.2:

"A "valid routable address" is a routable address which is either
statically assigned or whose lease
has not expired and that passes the
reachability test described in section 2 of "Detection of Network
Attachment (DNA) in IPv4" [DNAv4]."

"   When an interface has a valid routable address configured on an
   interface, the host SHOULD NOT also assign a Link-Local IPv4 address
   to that interface."

Again, the term "valid" is not helpful.  A host shouldn't have an invalid
address assigned on an interface, so the term "valid" has no use here
either.

"   If a host finds that an interface that was previous configured with a
   Link-Local IPv4 address is now configured with a valid routable
   address, the host MUST always use the routable address when
   initiating new communications, and MUST cease advertising the
   availability of the Link-Local IPv4 address through whatever
   mechanisms that address had been made known to others."

Again, the term "valid" is not needed here -- if the host has a routable
address configured, that's enough.

"Ways in which a valid routable address might be configured
   for the interface include:

   * Manual configuration
   * Address assignment through DHCP
   * Roaming of the host to a network on which a routable address
      assigned to the interface is valid

   If a host finds that an interface that was previously configured with
   a valid routable address no longer has a valid routable address, the
   host MAY identify a usable Link-Local IPv4 address (as described in
   section 2) and assign that address to the interface.  Ways in which a
   valid routable address might no longer be assigned to an interface
   include:

   * Removal of the address from the interface through manual
      configuration
   * Expiration of the lease on the address assigned through DHCP
   * Roaming of the host to a new network on which the address is no
     longer valid."

Here several uses of the term "valid" are not helpful.  Recommend changing
to:

"  Ways in which a routable address might be configured
   for the interface include:

   * Manual configuration
   * Address assignment through DHCP
   * Roaming of the host to a network on which the host has a valid
     routable address

   If a host finds that a routable address is no longer assigned to
   an interface,  the host MAY identify a usable Link-Local IPv4 address
   (as described in section 2) and assign that address to the interface.
   Ways in which a routable address might no longer be assigned to an
   interface include:

   * Removal of the address from the interface through manual
      configuration
   * Expiration of the lease on the address assigned through DHCP
   * Roaming of the host to a new network on which the address is no
     longer valid."