Update the bpf map read flag in system server

The previous bpf map read flag of map read helper function is set to
zero since the device kernel missed some bpf patches to do bpf read only
or write only operation. Now the patches are updated so system_server
should only use BPF_F_RDONLY to open the bpf maps.

Bug: 73777755
Test: run cts -m CtsNetTestCases -t android.net.cts.TrafficStatsTest
Change-Id: I55a1757bc3dc086ef5f54b773c2d362610bd416b