Cert: Fix cert security accepting any hci events

Some HciMatchers function where returning a function
that return a function instead of a function
that return a boolean. A function being a truthy value
in python, the matching function was accepting
anything given as input.

This bug hid an incorrect implementation
of CertSecurity.accept_pairing.

Test: gd/cert/run SecurityTest
Change-Id: I7f0cfaec6deb0361a3d1e7790b1158c2bcf5ebfd