Implement network-interface-* functions for MS-Windows (bug #15610).

Implement network-interface-* functions for MS-Windows (bug #15610).

 src/w32.c (network_interface_get_info, network_interface_list)
 (network_interface_info): New functions.
 (GetAdaptersInfo_Proc): New typedef.
 (get_adapters_info): New wrapper function.
 (globals_of_w32): Initialize g_b_init_get_adapters_info.
 src/process.h (network_interface_list, network_interface_info): New
 prototypes.
 src/process.c (conv_sockaddr_to_lisp): Now externally-visible.
 (Fnetwork_interface_list, Fnetwork_interface_info): Define for
 all systems.  Return non-nil for systems that HAVE_NET_IF_H and
 for WINDOWSNT.  Doc fix.
 (syms_of_process): Defsubr Snetwork_interface_list and
 Snetwork_interface_info unconditionally.