Use eBPF map data for per iface stats

After adding the xt_bpf module and ifaceStatsMap, eBPF tool can now
support reading per interface data. So networkStatsFactory should move
away from parsing proc/net/dev and use the eBPF map stats instead.

Bug: 72111305
Test: atest com.android.server.net.NetworkStatsServiceTest
Change-Id: Ibcc6150d00835b3bd33af22a72e4a86e172581cf