Create v4 mapped v6 correctly

Tests verifies the behavior with v4 mapped v6. The
taken parameter should be a v6 address. However,
InetAddresses.parseNumericAddress() will translate a v4
mapped v6 address into v4. This does not actually test
the behavior. The constant should be created via
Inet6Address.getByAddress() so that it will be an
expected Inet6Address.

Bug: 291869581
Test: atest NattKeepalivePacketDataTest
      w/ and w/o aosp/2626269
Change-Id: I2f086f0fe7d1dd038f5d850f2281deb807c837cf