PDL: Check subview size for checksums

When IsValid() calculates a checksum, it gets a SubView of the
packet.  Make sure that the SubView is a subset of the packet
before creating it.

Bug: 186612021
Test: atest bluetooth_test_gd_unit
Test: atest bluetooth_packet_parser_test
Change-Id: Iaadeec118134c172b9688859bdc8e10776833f01