use __socketcall to simplify socket()

commit 59324c8b09 added __socketcall
analogous to __syscall, returning the negated error rather than
setting errno. use it to simplify the fallback path of socket(),
avoiding extern calls and access to errno.

Author: Rich Felker <dalias@aerifal.cx>
Date:   Tue Jul 30 17:51:16 2019 -0400

    make __socketcall analogous to __syscall, error-returning

src/network/socket.c

@@ -5,17 +5,17 @@
 
 int socket(int domain, int type, int protocol)
 {
-	int s = socketcall(socket, domain, type, protocol, 0, 0, 0);
-	if (s<0 && (errno==EINVAL || errno==EPROTONOSUPPORT)
+	int s = __socketcall(socket, domain, type, protocol, 0, 0, 0);
+	if ((s==-EINVAL || s==-EPROTONOSUPPORT)
 	    && (type&(SOCK_CLOEXEC|SOCK_NONBLOCK))) {
-		s = socketcall(socket, domain,
+		s = __socketcall(socket, domain,
 			type & ~(SOCK_CLOEXEC|SOCK_NONBLOCK),
 			protocol, 0, 0, 0);
-		if (s < 0) return s;
+		if (s < 0) return __syscall_ret(s);
 		if (type & SOCK_CLOEXEC)
 			__syscall(SYS_fcntl, s, F_SETFD, FD_CLOEXEC);
 		if (type & SOCK_NONBLOCK)
 			__syscall(SYS_fcntl, s, F_SETFL, O_NONBLOCK);
 	}
-	return s;
+	return __syscall_ret(s);
 }