net/boinc-client: fix manager option depends, re-add manager default option back.
- BOINC manager needs wxWidgets 3.0.0 (since 7.4.0, see https://boinc.berkeley.edu/trac/wiki/SoftwarePrereqsUnix)
- Files boincmgr.*.png are at the other place.
PR: 225273
Reported by: olexander.v.melnyk@gmail.com