[Android] Remove repeated calls to beginHandshake

[simonrozsival]

On legacy Android APIs (26 and earlier) the SSLEngine.beginHandshake() Java method cannot be called when the handshake has already been started. This has been fixed in later Android revisions (which we use in CI).

There's a related problem: during the handshake process, the SSLSession isn't accessible and it's necessary to call the SSLEngine.getHandshakeSession() to get the reference to the session that's being constructed (see https://developer.android.com/reference/javax/net/ssl/SSLSocket#getHandshakeSession() for more info). That prompted several other changes in the pal_sslstream.c.

This PR fixes SslStream on Android APIs 24-26.

Closes #78716
Related to #77386

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Issue Details

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On legacy Android APIs (26 and earlier) the SSLEngine.beginHandshake() Java method cannot be called when the handshake has already been started. This has been fixed in later Android revisions (which we use in CI).

There's a related problem: during the handshake process, the SSLSession isn't accessible and it's necessary to call the SSLEngine.getHandshakeSession() to get the reference to the session that's being constructed (see https://developer.android.com/reference/javax/net/ssl/SSLSocket#getHandshakeSession() for more info). That prompted several other changes in the pal_sslstream.c.

Closes #78716
Related to #77386

Author:	simonrozsival
Assignees:	-
Labels:	area-System.Net.Security, os-android
Milestone:	-

[simonrozsival]

/azp run runtime-android

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[simonrozsival]

/azp run runtime-androidemulator

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[simonrozsival]

CI failures are unrelated to this PR.

[steveisok]

/backport to release/7.0

[steveisok]

/backport to release/6.0

[github-actions]

Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/3584440281

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/3584441419