Fixed compilation errors when configuring with with-subgrid=EAGLE and with-hydro=gizmo-mfv.

Another batch of errors flagged by @jbraspenning. This time there were some pj->masses being used in feedback_iact (despite mj = hydro_get_mass(pj) being defined). There were also some missing getters or getters with wrong arguments. And a missing include in hydro_iact.h.