Improve efficiency of network reads in TLSEngine

[mpilquist]

I was working with @tpolecat on testing Postgres TLS integration in skunk (#1897). While it's working now, Rob noticed lots of buffer underrun events during unwrapping as a result of requesting a single character from the TLSSocket. This turned in to a call to socket.read(1). Consequently, the TLSSocket#read1 implementation would read a single byte at a time from the underlying raw socket. This would continue until enough individual bytes had been read and queued that an unwrap operation could succeed.

In this PR, we guard against very small maxBytes by requesting up to session.getPacketBufferSize bytes from underlying socket when maxBytes is less than that value.

The result of the Postgres integration now completes with no underrun:

[info] Writing 8 byte(s).
[info] Reading 1 byte(s).
[info] Writing 132 byte(s).
[info] wrap result: Status = OK HandshakeStatus = NEED_UNWRAP
[info] bytesConsumed = 0 bytesProduced = 204
[info] unwrapHandshake result: Status = OK HandshakeStatus = NEED_TASK
[info] bytesConsumed = 66 bytesProduced = 0
[info] unwrapHandshake result: Status = OK HandshakeStatus = NEED_TASK
[info] bytesConsumed = 695 bytesProduced = 0
[info] unwrapHandshake result: Status = OK HandshakeStatus = NEED_TASK
[info] bytesConsumed = 338 bytesProduced = 0
[info] unwrapHandshake result: Status = OK HandshakeStatus = NEED_TASK
[info] bytesConsumed = 9 bytesProduced = 0
[info] unwrapHandshake result: Status = OK HandshakeStatus = NEED_WRAP
[info] bytesConsumed = 0 bytesProduced = 0
[info] wrapHandshake result: Status = OK HandshakeStatus = NEED_WRAP
[info] bytesConsumed = 0 bytesProduced = 75
[info] wrapHandshake result: Status = OK HandshakeStatus = NEED_WRAP
[info] bytesConsumed = 0 bytesProduced = 6
[info] wrapHandshake result: Status = OK HandshakeStatus = NEED_UNWRAP
[info] bytesConsumed = 0 bytesProduced = 45
[info] unwrapHandshake result: Status = OK HandshakeStatus = NEED_UNWRAP
[info] bytesConsumed = 6 bytesProduced = 0
[info] unwrapHandshake result: Status = OK HandshakeStatus = FINISHED
[info] bytesConsumed = 45 bytesProduced = 0
[info] wrap result: Status = OK HandshakeStatus = NOT_HANDSHAKING
[info] bytesConsumed = 132 bytesProduced = 161
[info] Reading 1 byte(s).
[info] unwrap result: Status = OK HandshakeStatus = NOT_HANDSHAKING
[info] bytesConsumed = 346 bytesProduced = 317
[info] Reading 4 byte(s).
[info] Reading 8 byte(s).
[info] <- 'R' (8 bytes)
[info] Terminating.

[tpolecat]

Very nice! 👍