Discard packets without fixed bit or reserved bits set.

Discard packets without fixed bit or reserved bits set.

Section 17.2 and 17.3 of QUIC transport:

Fixed bit: Packets containing a zero value for this bit are not
valid packets in this version and MUST be discarded.

Reserved bit: An endpoint MUST treat receipt of a packet that has
a non-zero value for these bits, after removing both packet and
header protection, as a connection error of type PROTOCOL_VIOLATION.