opensnoop: Refactor initial timestamp calculation
opensnoop: Refactor initial timestamp calculation

Signed-off-by: KarimAllah Ahmed <bc3bb9a24087248012a953aa758d020c025771a3@gmail.com>

iovisor/bcc,brendangregg/bcc,shodoco/bcc,mcaleavya/bcc,brendangregg/bcc,mkacik/bcc,romain-intel/bcc,brendangregg/bcc,iovisor/bcc,mkacik/bcc,mkacik/bcc,brendangregg/bcc,shodoco/bcc,shodoco/bcc,iovisor/bcc,tuxology/bcc,shodoco/bcc,romain-intel/bcc,mcaleavya/bcc,tuxology/bcc,tuxology/bcc,mcaleavya/bcc,shodoco/bcc,iovisor/bcc,mkacik/bcc,romain-intel/bcc,mkacik/bcc,mcaleavya/bcc,romain-intel/bcc,tuxology/bcc,mcaleavya/bcc,tuxology/bcc,brendangregg/bcc,iovisor/bcc,romain-intel/bcc