box: panic on OOM in port_c_add_*() methods

For easier maintenance, let's panic when there is no memory for allocation
needed to add a value to port - that's the approach we're taking right
now in Tarantool and we don't need to check return code of `port_c_add*()`
functions because they became non-failing. Functions from C API still
return int (which is always zero actually) for backward compatibility.

NO_TEST=no behavior changes
NO_CHANGELOG=no behavior changes
NO_DOC=no behavior changes