fix handshake failure handling

Change-Id: I43e0bd0b61d7ba2fd2409975fd40356dd017df59
allow for ZMTP 1.0 detection

ZMTP 2.0 peers set flags to 0x7F, but we were
asserting that that more flag was not set on the
identity frame.

Change-Id: I66b938cb2164179b8e5b3478a1524e7c1710bf46