BpfCoordinatorTest: add testDumpDoesNotCrash

Simple dump test for improving tethering test coverage.

Bug: 255466740
Test: atest BpfCoordinatorTest
Test: dump the content of testDump

Output:
mIsBpfEnabled: true
Polling not started
Stats provider registered
Upstream quota: {}
Polling interval: 5000 ms
Bpf shim: mBpfDownstream6Map{OK}, mBpfUpstream6Map{OK}, mBpfDownstream4Map{OK}, mBpfUpstream4Map{OK}, mBpfStatsMap{OK}, mBpfLimitMap{OK}, mBpfDevMap{OK}
Forwarding stats:
 <empty>
BPF stats:
 ifindex: 1001: rxPackets: 0, rxBytes: 0, rxErrors: 0, txPackets: 0, txBytes: 0, txErrors: 0

Forwarding rules:
 IPv6 Forwarding rules by downstream interface:
  [null]: iif(iface) oif(iface) v6addr [srcmac] [dstmac]
   1001(rmnet0) 1003(1003) 2001:db8::1 [12:34:56:78:90:ab] [00:00:00:00:00:0a]
 IPv6 Upstream: iif(iface) [inDstMac] -> oif(iface) etherType [outSrcMac] [outDstMac]
  1003(1003) [12:34:56:78:90:ab] -> 1001(rmnet0) 86dd [00:00:00:00:00:00] [00:00:00:00:00:00]
 IPv6 Downstream: iif(iface) [inDstMac] neigh6 -> oif(iface) etherType [outSrcMac] [outDstMac]
  1001(rmnet0) [00:00:00:00:00:00] 2001:db8::1 -> 1003(1003) 86dd [12:34:56:78:90:ab] [00:00:00:00:00:0a]
 IPv4 Upstream: proto [inDstMac] iif(iface) src -> nat -> dst [outDstMac] age
  tcp [12:34:56:78:90:ab] 1003(1003) 192.168.80.12:-3087 -> 1001(rmnet0) 1.0.0.1:-3087 -> 140.112.8.116:443 [00:00:00:00:00:00] -
 IPv4 Downstream: proto [inDstMac] iif(iface) src -> nat -> dst [outDstMac] age
  tcp [00:00:00:00:00:00] 1001(rmnet0) 140.112.8.116:443 -> 1003(1003) 1.0.0.1:-3087 -> 192.168.80.12:-3087 [00:00:00:00:00:0a] -

Device map:
 ifindex (iface) -> ifindex (iface)
  1001 (rmnet0) -> 1001 (rmnet0)
Client Information:
 <empty>
IPv4 Upstream Indices:
 <empty>

Forwarding counters:
 INVALID_IPV4_VERSION: 1000

Change-Id: I6346737157936cff7e164bbfe78d9a98dab3395a