kvm_nlist skips lookup for entries that have n_type != N_UNDF.
N_UNDF happens to be zero, so n_type typically has a correct
value by accident, but not always.
Note: jhb has a patch that replaces kvm_nlist use with direct
gdb parsing.
MFC after: 5 days
X-MFC-Note: unless jhb commits kvm_nlist => kgdb_parse change
c12959b335