LibC: Make <netinet/in.h> more POSIX compliant

1. Move htonl() etc. from <arpa/inet.h> to <netinet/in.h> (which
   <arpa/inet.h> includes).

   The htonl(), htons(), ntohl(), and ntohs() functions shall be
   available as described in <arpa/inet.h>.  Inclusion of the
   <netinet/in.h> header may also make visible all symbols from
   <arpa/inet.h>.

   - POSIX

2. Define IN6_IS_ADDR_LOOPBACK() and IN6_IS_ADDR_V4MAPPED()

Userland/Libraries/LibC/arpa/inet.h

@@ -6,7 +6,6 @@
 
 #pragma once
 
-#include <endian.h>
 #include <inttypes.h>
 #include <netinet/in.h>
 #include <sys/cdefs.h>
@@ -27,32 +26,4 @@ static inline int inet_aton(const char* cp, struct in_addr* inp)
 
 char* inet_ntoa(struct in_addr);
 
-static inline uint16_t htons(uint16_t value)
-{
-#if __BYTE_ORDER == __LITTLE_ENDIAN
-    return __builtin_bswap16(value);
-#else
-    return value;
-#endif
-}
-
-static inline uint16_t ntohs(uint16_t value)
-{
-    return htons(value);
-}
-
-static inline uint32_t htonl(uint32_t value)
-{
-#if __BYTE_ORDER == __LITTLE_ENDIAN
-    return __builtin_bswap32(value);
-#else
-    return value;
-#endif
-}
-
-static inline uint32_t ntohl(uint32_t value)
-{
-    return htonl(value);
-}
-
 __END_DECLS

Userland/Libraries/LibC/netinet/in.h

@@ -7,9 +7,44 @@
 #pragma once
 
 #include <Kernel/API/POSIX/netinet/in.h>
+#include <endian.h>
 
 __BEGIN_DECLS
 
 in_addr_t inet_addr(char const*);
 
+static inline uint16_t htons(uint16_t value)
+{
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+    return __builtin_bswap16(value);
+#else
+    return value;
+#endif
+}
+
+static inline uint16_t ntohs(uint16_t value)
+{
+    return htons(value);
+}
+
+static inline uint32_t htonl(uint32_t value)
+{
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+    return __builtin_bswap32(value);
+#else
+    return value;
+#endif
+}
+
+static inline uint32_t ntohl(uint32_t value)
+{
+    return htonl(value);
+}
+
+#define IN6_IS_ADDR_LOOPBACK(addr) \
+    (addr->s6_addr[0] == 0 && addr->s6_addr[1] == 0 && addr->s6_addr[2] == 0 && addr->s6_addr[3] == 0 && addr->s6_addr[4] == 0 && addr->s6_addr[5] == 0 && addr->s6_addr[6] == 0 && addr->s6_addr[7] == 0 && addr->s6_addr[8] == 0 && addr->s6_addr[9] == 0 && addr->s6_addr[10] == 0 && addr->s6_addr[11] == 0 && addr->s6_addr[12] == 0 && addr->s6_addr[13] == 0 && addr->s6_addr[14] == 0 && addr->s6_addr[15] == 1)
+
+#define IN6_IS_ADDR_V4MAPPED(addr) \
+    (addr->s6_addr[0] == 0 && addr->s6_addr[1] == 0 && addr->s6_addr[2] == 0 && addr->s6_addr[3] == 0 && addr->s6_addr[4] == 0 && addr->s6_addr[5] == 0 && addr->s6_addr[6] == 0 && addr->s6_addr[7] == 0 && addr->s6_addr[8] == 0xff && addr->s6_addr[9] == 0xff && addr->s6_addr[10] == 0xff && addr->s6_addr[11] == 0xff)
+
 __END_DECLS