Add network configuration API

[michaelrsweet]

Some users of PAPPL need greater control over the network configuration:

• Configuration mode: full manual (IP + netmask + router), manual IP + DHCP, and DHCP for IPv4 and IPv6
• Enable/disable network interfaces
• Auto/manual DNS servers and domains

Essentially we should provide a similar level of UI as the macOS Network preference pane.

As for Wi-Fi configuration, there should be a new API for getting and setting the current network configuration since the mechanism varies based on OS/distro.

[michaelrsweet]

Created a new network branch to develop this on...

[michaelrsweet]

Proposed API:

typedef enum pappl_netconf_e            // Network configuration mode
{
  PAPPL_NETCONF_OFF,                            // Turn network interface off
  PAPPL_NETCONF_DHCP,                           // Full DHCP
  PAPPL_NETCONF_DHCP_MANUAL,                    // DHCP with manual IP address
  PAPPL_NETCONF_MANUAL                          // Manual IP, netmask, and router
} pappl_netconf_t;

typedef struct pappl_network_s          // Network interface information
{
  char                  name[64];               // Interface name
  bool                  up;                     // Is this interface up (read-only)?
  pappl_netconf_t       config4;                // IPv4 configuration mode
  struct sockaddr_in    addr4,                  // IPv4 address
                        mask4,                  // IPv4 netmask
                        router4,                // IPv4 router address
                        dns4[2];                // IPv4 DNS addresses
  pappl_netconf_t       config6;                // IPv6 configuration mode
  struct sockaddr_in6   linkaddr6,              // IPv6 link-local address (read-only)
                        addr6,                  // IPv6 address
                        mask6,                  // IPv6 netmask
                        router6,                // IPv6 router address
                        dns6[2];                // IPv6 DNS addresses
} pappl_network_t;

// Get networks callback
typedef size_t (*pappl_network_get_cb_t)(pappl_system_t *system, void *cb_data, size_t max_networks, pappl_network_t *networks);

// Set networks callback
typedef bool (*pappl_network_set_cb_t)(pappl_system_t *system, void *cb_data, size_t num_networks, pappl_network_t *networks);

// Set network callbacks
extern void papplSystemSetNetworkCallbacks(pappl_system_t *system, pappl_network_get_cb_t get_cb, pappl_network_set_cb_t set_cb, void *cb_data) _PAPPL_PUBLIC;

[michaelrsweet]

[network 21936d9] Initial network configuration API (Issue #217)