Fix initialization and re-computation of expirationTimestamp in Http2ClientConnectionImpl

[ahus1]

Closes #5865

Motivation:

Setting expirationTimestamp is required before the connection is recycled to ensure that the background timer executed correctly.

In a previous attempt I tried to set the initial value to Long.MAX_VALUE, but then Http2Test.testClientKeepAliveTimeoutNoStreams started failing. So I'm no setting it a value using recycle().

[vietj]

@ahus1 is that possible to have a test for this ?

[ahus1]

@vietj - this is fixing an unstable test that I referenced in the issue #5865. As it is about a timing issue, I wouldn't know how to implement a test case for this.

Can you please elaborate on what kind if test case you are looking for?