re: Make sure re_rxeof() is called in net epoch context

It may pass packets up the stack and so needs to be called in a network
epoch. When a watchdog timeout happens, we need to enter a section
explicitly.

Reviewed by: zlei, glebius, adrian
MFC after: 2 weeks
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D51885

(cherry picked from commit b653a281f5a977ba73b3d405874f8af8e8b6b50d)