Set rxinfo.epoch from the epoch, and then assign it to ts.secs; that

Set rxinfo.epoch from the epoch, and then assign it to ts.secs; that
avoids doing a narrowing case - which, in this case, is safe
(rxinfo.epoch is 32 bits, and the value assigned to it is 32 bits, so
it's not as if it'd ever be wider than 32 bits even if ts.secs is wider
than 32 bits), but you might still have to think about it.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@24658 f5534014-38df-0310-8fa8-9805f1628bb7