selftests: mptcp: fix typo in mptcp_connect usage

in mptcp_connect, 's' selects IPPROTO_MPTCP / IPPROTO_TCP as the value of
'protocol' in socket(), and 'm' switches between different send / receive
modes. Fix die_usage(): swap 'm' and 's' and add missing 'sendfile' mode.
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/mptcp/mptcp_connect.c

@@ -65,8 +65,8 @@ static void die_usage(void)
 	fprintf(stderr, "\t-S num -- set SO_SNDBUF to num\n");
 	fprintf(stderr, "\t-R num -- set SO_RCVBUF to num\n");
 	fprintf(stderr, "\t-p num -- use port num\n");
-	fprintf(stderr, "\t-m [MPTCP|TCP] -- use tcp or mptcp sockets\n");
-	fprintf(stderr, "\t-s [mmap|poll] -- use poll (default) or mmap\n");
+	fprintf(stderr, "\t-s [MPTCP|TCP] -- use mptcp(default) or tcp sockets\n");
+	fprintf(stderr, "\t-m [poll|mmap|sendfile] -- use poll(default)/mmap+write/sendfile\n");
 	fprintf(stderr, "\t-u -- check mptcp ulp\n");
 	fprintf(stderr, "\t-w num -- wait num sec before closing the socket\n");
 	exit(1);