Rename min_response_window to init_delay

Rename main_config's "min_response_window" field to "init_delay", as it
better reflects the usage and because its value won't be related to any
response window in case they're all higher than 1/3 s, which is true
most of the time.
Fix cf_item_parse calls in bfd
Whitespace changes
Simplify masking
Add nonnull hint
Add fr_ptonx, fr_ntop and is_wildcard IP address functions
Switch to using fr_ipaddr_t for client prefixes, and allow ipaddr and ipaddr6 config items to be prefixes. Addresses #581.
Add fr_ipaddr_mask to fixup fr_ipaddr_t's by zeroing out the host portion of the address
Minor typos in error messages
Fix issue where use of FreeRADIUS-Client-IPv6-Prefix and FreeRADIUS-Client-IPv4-Prefix when creating dynamic client entries, would trigger an error.
Fixup fake client for proto_arp
Rename fr_pton functions to fr_pton4, fr_pton6 and fr_pton. fr_pton will resolve the IP address to either 4 or 6 based on format and/or available DNS records.
Add PW_TYPE_COMBO_IP_PREFIX (conffile parser only)

Change 'ipaddr' to PW_TYPE_COMBO_IP_PREFIX so we can be really lazy about IP formats
Rename PW_TYPE_IP* so they're all consistent
Add similar ipaddr, ipv4addr, ipv6addr config items for listen sections
Update warning for clients
Add similar ipaddr, ipv4addr, ipv6addr config items for realms
Don't try to resolve IPv6 addresses in fr_pton
Remove support for old style client definitions (master only)
Remove deprecated methods of specifying clients from clients.conf