Fix warnings with `-Wunused-function`

[Nikita240]

When including this header library into an application that is compiled with -Wunused-function or -Wall, the compiler spews tons of warnings.

../dependencies/mdns/mdns.h:1487:1: warning: 'size_t mdns_record_parse_txt(const void*, size_t, size_t, size_t, mdns_record_txt_t*, size_t)' defined but not used [-Wunused-function]
 1487 | mdns_record_parse_txt(const void* buffer, size_t size, size_t offset, size_t length,
      | ^~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1474:1: warning: 'sockaddr_in6* mdns_record_parse_aaaa(const void*, size_t, size_t, size_t, sockaddr_in6*)' defined but not used [-Wunused-function]
 1474 | mdns_record_parse_aaaa(const void* buffer, size_t size, size_t offset, size_t length,
      | ^~~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1439:1: warning: 'mdns_record_srv_t mdns_record_parse_srv(const void*, size_t, size_t, size_t, char*, size_t)' defined but not used [-Wunused-function]
 1439 | mdns_record_parse_srv(const void* buffer, size_t size, size_t offset, size_t length,
      | ^~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1429:1: warning: 'mdns_string_t mdns_record_parse_ptr(const void*, size_t, size_t, size_t, char*, size_t)' defined but not used [-Wunused-function]
 1429 | mdns_record_parse_ptr(const void* buffer, size_t size, size_t offset, size_t length,
      | ^~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1420:1: warning: 'int mdns_goodbye_multicast(int, void*, size_t, mdns_record_t, mdns_record_t*, size_t, mdns_record_t*, size_t)' defined but not used [-Wunused-function]
 1420 | mdns_goodbye_multicast(int sock, void* buffer, size_t capacity, mdns_record_t answer,
      | ^~~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1411:1: warning: 'int mdns_announce_multicast(int, void*, size_t, mdns_record_t, mdns_record_t*, size_t, mdns_record_t*, size_t)' defined but not used [-Wunused-function]
 1411 | mdns_announce_multicast(int sock, void* buffer, size_t capacity, mdns_record_t answer,
      | ^~~~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1402:1: warning: 'int mdns_query_answer_multicast(int, void*, size_t, mdns_record_t, mdns_record_t*, size_t, mdns_record_t*, size_t)' defined but not used [-Wunused-function]
 1402 | mdns_query_answer_multicast(int sock, void* buffer, size_t capacity, mdns_record_t answer,
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:1300:1: warning: 'int mdns_query_answer_unicast(int, const void*, size_t, void*, size_t, uint16_t, mdns_record_type_t, const char*, size_t, mdns_record_t, mdns_record_t*, size_t, mdns_record_t*, size_t)' defined but not used [-Wunused-function]
 1300 | mdns_query_answer_unicast(int sock, const void* address, size_t address_size, void* buffer,
      | ^~~~~~~~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:959:1: warning: 'size_t mdns_socket_listen(int, void*, size_t, mdns_record_callback_fn, void*)' defined but not used [-Wunused-function]
  959 | mdns_socket_listen(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
      | ^~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:855:1: warning: 'size_t mdns_discovery_recv(int, void*, size_t, mdns_record_callback_fn, void*)' defined but not used [-Wunused-function]
  855 | mdns_discovery_recv(int sock, void* buffer, size_t capacity, mdns_record_callback_fn callback,
      | ^~~~~~~~~~~~~~~~~~~
../dependencies/mdns/mdns.h:850:1: warning: 'int mdns_discovery_send(int)' defined but not used [-Wunused-function]
  850 | mdns_discovery_send(int sock) {

This is due to the usage of non-inline static functions in the header.

The solution is to convert all the functions to static inline.

[mjansson]

Makes sense