MINOR: quic: Drop packet with type for discarded packet number space.

MINOR: quic: Drop packet with type for discarded packet number space.

This patch allows the low level packet parser to drop packets with type for discarded
packet number spaces. Furthermore, this prevents it from reallocating new encryption
levels and packet number spaces already released/discarded. When a packet number space
is discarded, it MUST NOT be reallocated.

As the packet number space discarding is done asap the type of packet received is
known, some packet number space discarding check may be safely removed from qc_try_rm_hp()
and qc_qel_may_rm_hp() which are called after having parse the packet header, and
is type.