net/tls: Make function tls_sw_do_sendpage static

Fixes the following sparse warning:

 net/tls/tls_sw.c:1023:5: warning:
 symbol 'tls_sw_do_sendpage' was not declared. Should it be static?
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_sw.c

@@ -1020,7 +1020,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 	return copied ? copied : ret;
 }
 
-int tls_sw_do_sendpage(struct sock *sk, struct page *page,
+static int tls_sw_do_sendpage(struct sock *sk, struct page *page,
 			      int offset, size_t size, int flags)
 {
 	long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);