Merge #21328: net, refactor: pass uint16 CService::port as uint16

52dd40a9fe test: add missing netaddress include headers (Jon Atack)
6f09c0f6b5 util: add missing braces and apply clang format to SplitHostPort() (Jon Atack)
2875a764f7 util: add ParseUInt16(), use it in SplitHostPort() (Jon Atack)
6423c8175f p2p, refactor: pass and use uint16_t CService::port as uint16_t (Jon Atack)

Pull request description:

  As noticed during review today in https://github.com/bitcoin/bitcoin/pull/20685#discussion_r584873708 of the upcoming I2P network support, `CService::port` is `uint16_t` but is passed around the codebase and into the ctors as `int`, which causes uneeded conversions and casts. We can avoid these (including in the incoming I2P code without further changes to it) by using ports with the correct type. The remaining conversions are pushed out to the user input boundaries where they can be range-checked and raise with user feedback in the next patch.

ACKs for top commit:
  practicalswift:
    cr ACK 52dd40a9fe: patch looks correct
  MarcoFalke:
    cr ACK 52dd40a9fe
  vasild:
    ACK 52dd40a9fe

Tree-SHA512: 203c1cab3189a206c55ecada77b9548b810281cdc533252b8e3330ae0606b467731c75f730ce9deb07cbaab66facf97e1ffd2051084ff9077cba6750366b0432

src/test/net_tests.cpp

@@ -8,6 +8,7 @@
 #include <clientversion.h>
 #include <cstdint>
 #include <net.h>
+#include <netaddress.h>
 #include <netbase.h>
 #include <serialize.h>
 #include <span.h>
@@ -91,7 +92,7 @@ BOOST_FIXTURE_TEST_SUITE(net_tests, BasicTestingSetup)
 BOOST_AUTO_TEST_CASE(cnode_listen_port)
 {
     // test default
-    uint16_t port = GetListenPort();
+    uint16_t port{GetListenPort()};
     BOOST_CHECK(port == Params().GetDefaultPort());
     // test set port
     uint16_t altPort = 12345;