Fix NetdHidlTest.TestAddRemoveInterfaces()

Fix NetdHidlTest.TestAddRemoveInterfaces()

The regex in countRulesForFwmark() overeagerly matched rules ending
in the same hex digit. For instance, fwmark=3 would match both these
lines:

  from all fwmark 0xd0003/0xdffff iif lo lookup netd13474_27190
  from all fwmark 0x10063/0x1ffff iif lo lookup local_network

This fix consists in matching either just 0x3, or the zero-padded 0003.

Bug: 74922133
Test: as follows:
    m VtsHalNetNetdV1_1TargetTest && \
    adb push out/.../VtsHalNetNetdV1_1TargetTest /data/ && \
    adb shell /data/VtsHalNetNetdV1_1TargetTest
Change-Id: If6df9fa6cf843a5593ce61d87366c23383bb4d81