quic: fix Identification field being always 0

Fixes a classic C typo with (*ptr++) syntax.
The bug resulted in all Firedancer QUIC packets having an IPv4 ID
field of 0.  Most Internet peers (most notably Linux) are resilient
enough to handle this.  Should be fixed nonetheless.

src/waltz/quic/fd_quic.c

@@ -2951,7 +2951,7 @@ fd_quic_tx_buffered_raw(
   pkt.ip4->verihl       = FD_IP4_VERIHL(4,5);
   pkt.ip4->tos          = (uchar)(config->net.dscp << 2); /* could make this per-connection or per-stream */
   pkt.ip4->net_tot_len  = (ushort)( 20 + 8 + payload_sz );
-  pkt.ip4->net_id       = *ipv4_id++;
+  pkt.ip4->net_id       = *ipv4_id;
   pkt.ip4->net_frag_off = 0x4000u; /* don't fragment */
   pkt.ip4->ttl          = 64; /* TODO make configurable */
   pkt.ip4->protocol     = FD_IP4_HDR_PROTOCOL_UDP;
@@ -2960,6 +2960,7 @@ fd_quic_tx_buffered_raw(
   pkt.udp->net_dport    = dst_udp_port;
   pkt.udp->net_len      = (ushort)( 8 + payload_sz );
   pkt.udp->check        = 0x0000;
+  *ipv4_id = (ushort)( *ipv4_id + 1 );
 
   /* TODO saddr could be zero -- should use the kernel routing table to
      determine an appropriate source address */