To speed up packet processing and also avoid grabbing the prison
mutex in SMR section (a regression from de2d47842e8) allocate and
free prison address lists with the network epoch protection:
o Provide functions prison_ip_alloc()/prison_ip_free() that would
prepend epoch context to the array of addresses.
o Merge prison_restrict_ip into address family agnostic
prison_ip_restrict(). This new function also differs from the old ones that it doesn't edit address arrays in place, but rather always allocates (or uses pre-allocated) new array of addresses, to guarantee stability of the old list to epoch-protected readers.
o prison_check_ip_locked now assert thay either prison mutex is held
or we are in the network epoch.