Ensure repeated connections are captured

std::map::emplace does not replace existing value if the key
already exists.

The newly constructed element will be destroyed immediately
if there already is an element with the key in the container.

Bug: 235872679
Tag: #test
Test: gd/cert/run --sl4a --clean

Change-Id: I340b723e805c0b94128bf6665690571f09dc9529