Kernel/LibC: Implement socketpair for UNIX sockets

userspace/libraries/LibC/include/sys/syscall.h

@@ -64,6 +64,7 @@ __BEGIN_DECLS
 	O(SYS_FCHOWNAT,			fchownat)		\
 	O(SYS_LOAD_KEYMAP,		load_keymap)	\
 	O(SYS_SOCKET,			socket)			\
+	O(SYS_SOCKETPAIR,		socketpair)		\
 	O(SYS_BIND,				bind)			\
 	O(SYS_SENDTO,			sendto)			\
 	O(SYS_RECVFROM,			recvfrom)		\

userspace/libraries/LibC/sys/socket.cpp

@@ -68,6 +68,11 @@ int socket(int domain, int type, int protocol)
 	return syscall(SYS_SOCKET, domain, type, protocol);
 }
 
+int socketpair(int domain, int type, int protocol, int socket_vector[2])
+{
+	return syscall(SYS_SOCKETPAIR, domain, type, protocol, socket_vector);
+}
+
 int getsockname(int socket, struct sockaddr* __restrict address, socklen_t* __restrict address_len)
 {
 	return syscall(SYS_GETSOCKNAME, socket, address, address_len);