Fix missing rename

MSP-9228

When Msf::Payload#offsets was renamed to
Msf::Payload#offset_relative_address_and_type_by_name, I failed to
rename Msf::Payload::Stager#offsets to
Msf::Payload::Stager#offset_relative_address_and_type_by_name, which
resulted in staged payload like linux/x86/shell/reverse_tcp having nil
offset_relative_address_and_type_by_name in
Msf::Payload#internal_generate, which resulted in the staged payload not
being able to connect back to the local host.