rmnet_perf: reset stored IP flags on forced flush

RmNet perf module only stores IP-specific fields such as TOS, TTL,
or Traffic Class when the flow node is allocated. If these fields
ever change over the course of a flow, we will continuously force
flushes due to flag mismatches on these subsequent packets and will
not coalesce them.

To fix this issue, we must update these IP fields within the flow_node
structure when we force a flush with flush_pkt_now due to header
field mismatches.

Change-Id: I0279f039ce14b962f43ecc78b56cf51e3a479818
CRs-Fixed: 2311643