Bugfix release

• [BUGFIX] client: don't call ignore_init() in middle of batch send. ignore_init() makes an assumption that the send controller has access to all outgoing packets. This change wraps a few IETF full connection methods to delay calling ignore_init() until the engine returns all outgoing packets that were batched.
• [BUGFIX] set errno to EAGAIN if sendmmsg() can't send all of them. This needs to be done because the value of errno may be lost on some platforms.
• [BUGFIX] Typo that set all bits in sm_qflags lead to crashes.
• [BUGFIX] Do not cancel header block processing after failure, as QPACK releases the reference in that case.
• [CLEANUP] IETF encrypt: replace assert(0) with a warning.
• Several small improvements to the test server.