SSH: add protocol lock direction

Some protocols have to call the underlying functions without regard to
what exact state the socket signals. For example even if the socket says
"readable", the send function might need to be called while uploading,
or vice versa. This is the case for libssh2 based protocols: SCP and
SFTP and we now introduce a define to set those protocols and we make
the multi interface code aware of this concept.

This is another fix to make test 582 run properly.