DO-NOT-MERGE: mptcp: enabled by default

This commit is useful for automated builds, e.g. from Intel's kbuild.

Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
diff --git a/net/mptcp/Kconfig b/net/mptcp/Kconfig
index 2032892..10c97e1 100644
--- a/net/mptcp/Kconfig
+++ b/net/mptcp/Kconfig
@@ -5,6 +5,7 @@
 	select SKB_EXTENSIONS
 	select CRYPTO_LIB_SHA256
 	select CRYPTO
+	default y
 	help
 	  Multipath TCP (MPTCP) connections send and receive data over multiple
 	  subflows in order to utilize multiple network paths. Each subflow