Enable Multipath TCP support

See https://www.mptcp.dev/ for MPTCP details and OTP 27.3.4.6 for use
when Erlang.

Author: fhunleth

linux-6.12.defconfig

@@ -20,6 +20,7 @@ CONFIG_IP_ADVANCED_ROUTER=y
 CONFIG_IP_MULTIPLE_TABLES=y
 # CONFIG_INET_DIAG is not set
 # CONFIG_IPV6_SIT is not set
+CONFIG_MPTCP=y
 CONFIG_PCI=y
 CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y