BUG/MEDIUM: tools: do not force an unresolved address to AF_INET:0.0.0.0

BUG/MEDIUM: tools: do not force an unresolved address to AF_INET:0.0.0.0

This prevents DNS from resolving IPv6-only servers in 1.7. Note, this
patch depends on the previous series :

  1. BUG/MINOR: tools: fix off-by-one in port size check
  2. BUG/MEDIUM: server: consider AF_UNSPEC as a valid address family
  3. MEDIUM: server: split the address and the port into two different fields
  4. MINOR: tools: make str2sa_range() return the port in a separate argument
  5. MINOR: server: take the destination port from the port field, not the addr
  6. MEDIUM: server: disable protocol validations when the server doesn't resolve

This fix (hence the whole series) must be backported to 1.7.