BUG/MINOR: h3: only increment frame type counter on new header

BUG/MINOR: h3: only increment frame type counter on new header

For every new HTTP/3 received frame, a counter related to the frame type
is incremented. This operation is performed directly in h3_rcv_buf()
parsing loop.

Prior to this patch, increment would be called too many times when
dealing with large frames. Fix this by ensuring that the increment is
only reported once per frame. This is now performed directly after
HTTP/3 frame header parsing.

This must be backported up to 2.6.