usnic: return 0 from eq_sread upon timeout

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
fi_eq: specify that sread returns 0 upon timeout

This seems to be the intended behavior, judging from the verbs and
sockets providers.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
Merge pull request #268 from jsquyres/pr/man-fi-eq-timeout-updates

Clarify fi_eq.3 that fi_eq_sread() returns 0 upon timeout