Fix mutex-lock-ordering

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Fix: Correctly initialize rcvbuf

Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Fix: unused variable warning

Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>
Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
/proc/net/mptcp does not depend on sysctl

Signed-off-by: Gregory Detal <gregory.detal@uclouvain.be>
Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>