BUG/MINOR: qpack: reject invalid dynamic table capacity

BUG/MINOR: qpack: reject invalid dynamic table capacity

Currently haproxy does not implement dynamic table support for QPACK. As
such, dynamic table capacity advertized via H3 SETTINGS is 0. When
receiving a non-null Set Dynamic Table Capacity instruction, close
immediately the connection using QPACK_ENCODER_STREAM_ERROR.

Prior to this patch, such instructions were simply ignored. This is non
conform to QUIC specification.

This should be backported up to 2.6. Note that on 2.6 qcc_set_error()
must be replaced by function qcc_emit_cc_app().