man(1) needs to check for .so files not only in the first line
PR: 279182

Some manual pages have a copyright notice or commit id before including
other files with the .so macro. We need to skip comments and empty lines
at the beginning of the manpage while checking for the first .so macro.

MFC after: 1 week

(cherry picked from commit 73eb53813fe3a2245edbeb670902e4bb9d41e288)