GlusterFS: fix OSX compilation failure

ged0b19b introduced support for 64 bits bitmask. Make use of it and add an explicit cast to fix a compilation error

Change-Id: I9f2202d851aedc0dc78655c505b5a0b26b224c0e
Reviewed-on: https://code.wireshark.org/review/4630
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Tested-by: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>