Fix IPv6 client IPs when the proxy uses KeepAlive

[BenSjoberg]

I think I figured out #37. It's because of how the original apr_sockaddr_t object is restored to the request_rec object during the cleanup process.

When a request is being processed, the original IP address is saved and the apr_sockaddr_t object is overwritten with a new one based on the IP in X-Forwarded for:

rpaf_cleanup_rec *rcr = (rpaf_cleanup_rec *)apr_pcalloc(r->pool, sizeof(rpaf_cleanup_rec));
rcr->old_ip = apr_pstrdup(r->DEF_POOL, r->DEF_IP);
rcr->r = r;
apr_pool_cleanup_register(r->pool, (void *)rcr, rpaf_cleanup, apr_pool_cleanup_null);
r->DEF_IP = apr_pstrdup(r->DEF_POOL, last_val);
memcpy(&rcr->old_addr, r->DEF_ADDR, sizeof(apr_sockaddr_t));

tmppool = r->DEF_ADDR->pool;
tmpport = r->DEF_ADDR->port;
apr_sockaddr_t *tmpsa;
int ret = apr_sockaddr_info_get(&tmpsa, r->DEF_IP, APR_UNSPEC, tmpport, 0, tmppool);
if (ret == APR_SUCCESS)
    memcpy(r->DEF_ADDR, tmpsa, sizeof(apr_sockaddr_t));

Then during the cleanup, rcr->old_ip is used to put the original IP address back into r->DEST_ADDR:

rcr->r->DEF_ADDR->sa.sin.sin_addr.s_addr = apr_inet_addr(rcr->r->DEF_IP);

The problem is that when X-Forwarded-For contains an IPv6 address, r->DEF_ADDR->family is set to APR_INET6. When the connection is reused, r->DEF_ADDR is checked against RPAF_ProxyIPs to see if it's an authorized proxy, but it thinks it's checking against an IPv6 address, so it doesn't match. (If RPAF_ProxyIPs isn't set, this problem doesn't happen.)

Another problem is that apr_inet_addr() doesn't support IPv6 addresses, so the current code would also have issues when IPv6 is used to communicate with the proxy. Instead of reconstructing the address from r->DEF_IP, my solution is to just copy r->DEF_ADDR into a new member of rpaf_cleanup_rec, then copy it back during the cleanup process.

[gnif]

Nice clean solution! Thanks!