MINOR: mux-quic: close on frame alloc failure

MINOR: mux-quic: close on frame alloc failure

Replace all BUG_ON() on frame allocation failure by a CONNECTION_CLOSE
sending with INTERNAL_ERROR code. This can happen for the following
cases :
* sending of MAX_STREAM_DATA
* sending of MAX_DATA
* sending of MAX_STREAMS_BIDI

In other cases (STREAM, STOP_SENDING, RESET_STREAM), an allocation
failure will only result in the current operation to be interrupted and
retried later. However, it may be desirable in the future to replace
this with a simpler CONNECTION_CLOSE emission to recover better under a
memory pressure issue.

This should be backported up to 2.7.