ITS#8654 - Option for LDAP client to bind to a local address

[Daniel Le <daniel.le@exfo.com>]

Hello,

In reference to the enhancement request ITS#865, please comment on the following to add support for binding a local IP address to client socket. This is just an outline of changes for one local address. I am not sure whether a list of local addresses is necessary. If it is, then a new function, similarly to ldap_url_parsehosts, may be written to parse the list of local addresses and store them into a linked list. In my use case, only one IPv4 or IPv6 local address is used for binding.

- Modify ldap.h and ldap_set_option to handle the new option LDAP_OPT_LOCAL_ADDRESS.
   Should it be named LDAP_OPT_CLIENT_ADDRESS, LDAP_OPT_SOCKET_BIND_ADDRESS...?

- Modify struct ldapoptions in ldap-int.h to add element "char *ldo_local_address" to hold client local address when ldap_set_option(LDAP_OPT_LOCAL_ADDRESS...) is executed.
  This can char pointer can point to an IPv4 address or IPv6 address.

- ldap_connect_to_host() in os-ip.c 
  After the connection socket is created (ldap_int_socket) and before it is connected (ldap_pvt_connect), extract the local IP address.
  If local address family (AF_INET/ AF_INET6) matches the one of the host, bind socket to the local address.

Regards,
Daniel