devel/electron13: fix obtaining HOST_NAME_MAX

Using sysconf(3) API lead to accidental introduction of variable
length arrays (VLA) in the port. Additionally gethostname(3) has been
passed _SC_HOST_NAME_MAX incorrectly as the HOST_NAME_MAX length.

Fall back to using _POSIX_HOST_NAME_MAX as the remaining code is not
ready for introducing sysconf(3) as a patch.

Bump PORTREVISION to rebuild with the new patch.

The patch was lifted from www/chromium which has a similar diff
pending.

Sponsored by: Fudo Security
Differential Revision: https://reviews.freebsd.org/D30064