UCP/GTEST: rndv - fix the case where the rts is received on a stub ep.
UCP/GTEST: rndv - fix the case where the rts is received on a stub ep.

in this case, try to perform get_zcopy. if cannot, swtich to AM rndv.

sergsagal1/ucx_rocm,shssf/ucx,sergsagal1/ucx_rocm,shssf/ucx,shssf/ucx,sergsagal1/ucx_rocm