Don't set cur=inf RLIM_NOFILE on macOS

Don't set cur=inf RLIM_NOFILE on macOS

virProcessActivateMaxFiles sets rlim_cur to rlim_max.
If rlim_max is RLIM_INFINITY,

2023-08-15 15:17:51.944+0000: 4456752640: debug :
virProcessActivateMaxFiles:1067 : Initial max files was 2560
2023-08-15 15:17:51.944+0000: 4456752640: debug :
virProcessActivateMaxFiles:1077 : Raised max files to
9223372036854775807

then when virCommandMassClose does `int openmax = sysconf(
_SC_OPEN_MAX)`, `openmax < 0` is true and virCommandMassClose
reports an error and bails.  Setting rlim_cur instead to at most
OPEN_MAX, as macOS' documentation suggests, both avoids this problem

2023-08-18 16:01:44.366+0000: 4359562752: debug :
virProcessActivateMaxFiles:1072 : Initial max files was 256
2023-08-18 16:01:44.366+0000: 4359562752: debug :
virProcessActivateMaxFiles:1086 : Raised max files to 10240

and eliminates a case of what the documentation declares
to be invalid input to setrlimit anyway.

Signed-off-by: Laura Hild <lsh@jlab.org>