Explicitly lengthen some constants to 64 bits

Hopefully squashes the mac buildbot error

packet-mp2t.c:993: warning: implicit conversion shortens 64-bit value into a
32-bit value

Change-Id: I9ca6420925442b56cfdf5db629b63d6ead7bdfbd
Reviewed-on: https://code.wireshark.org/review/4045
Reviewed-by: Evan Huus <eapache@gmail.com>