selftests/net: tcp_mmap: fix clang warning for target arch PowerPC

When size_t maps to unsigned int (e.g. on 32-bit powerpc), then the
comparison with 1<<35 is always true. Clang 9 threw:
warning: result of comparison of constant 34359738368 with \
expression of type 'size_t' (aka 'unsigned int') is always true \
[-Wtautological-constant-out-of-range-compare]
        while (total < FILE_SZ) {

Tested: make -C tools/testing/selftests TARGETS="net" run_tests

Fixes: 192dc405 ("selftests: net: add tcp_mmap program")
Signed-off-by: Tanner Love <tannerlove@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/tcp_mmap.c

@@ -344,7 +344,7 @@ int main(int argc, char *argv[])
 {
 	struct sockaddr_storage listenaddr, addr;
 	unsigned int max_pacing_rate = 0;
-	size_t total = 0;
+	uint64_t total = 0;
 	char *host = NULL;
 	int fd, c, on = 1;
 	char *buffer;
@@ -473,12 +473,12 @@ int main(int argc, char *argv[])
 		zflg = 0;
 	}
 	while (total < FILE_SZ) {
-		ssize_t wr = FILE_SZ - total;
+		int64_t wr = FILE_SZ - total;
 
 		if (wr > chunk_size)
 			wr = chunk_size;
 		/* Note : we just want to fill the pipe with 0 bytes */
-		wr = send(fd, buffer, wr, zflg ? MSG_ZEROCOPY : 0);
+		wr = send(fd, buffer, (size_t)wr, zflg ? MSG_ZEROCOPY : 0);
 		if (wr <= 0)
 			break;
 		total += wr;