ssa.c: Add read/write length checking on internal socketpairs

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
ssa.c: Eliminate a couple of errors now detected for consumer (ACM) nodes

The errors in the ACM log are:
[CTRL]: ssa_ctrl_port_send: ERROR - -1 out of 12 bytes written to downstream
[CTRL]: ssa_ctrl_send_listen: ERROR - -1 out of 16 bytes written

This is because consumer (ACM) nodes do not have downstream.
These are innocuous errors for consumer (ACM) nodes but
are eliminated by this patch.

First error is eliminated by making sure that node type is not consumer
before sending message in ssa_ctrl_port_send.

Second error is eliminated by checking for node type other than
consumer before calling ssa_ctrl_send_listen in ssa_ctrl_port.

Signed-off-by: Hal Rosenstock <hal@mellanox.com>