extattr_get_file(2): sort syscalls alphabetically

Although some sections of the manpage sort the syscalls alphabetically, many
core areas of the manpage do not. Sort the syscalls so it is easier to pick out
functional changes and to improve manpage readability.

This formatting change is also being done to make future functional changes
easier to spot.

MFC after: 1 week
Sponsored by: DellEMC Isilon