Add conditional check for interface type in PDI creation

[tariromukute]

Description:

The N6 PDI (Packet Detection Information) should not include a bogus S1-U interface type. Currently, the source interface type is being set unconditionally, which causes issues when creating PDIs for certain edge types.

Problem:

In src/smf_app/smf_procedure.cpp, the pdi.set(source_interface_type) is called without checking if a valid interface type has been set for the edge. This means the N6 PDI may carry an invalid S1-U interface type.

Solution:

Implement a conditional check using a flag (e.g., have_interface_type) to only set the source interface type in the PDI when it has been explicitly set for valid edge types (N3 3GPP Access and N9).

Suggested Implementation:

bool have_interface_type = false;
if (edge->type == n3_type) {
  // TS 29.244 Table 8.2.118-1: 11 = N3 3GPP Access.
  // 14 (N3 for data forwarding) is for indirect forwarding tunnels only.
  source_interface_type.interface_type_value =
      pfcp::_3GPP_INTERFACE_TYPE_N3_3GPP_ACCESS;
  have_interface_type = true;
} else if (edge->type == n9_type) {
  source_interface_type.interface_type_value = pfcp::_3GPP_INTERFACE_TYPE_N9;
  have_interface_type = true;
}

// Later, when setting PDI:
if (have_interface_type) {
  pdi.set(source_interface_type);
}

File: src/smf_app/smf_procedure.cpp