Added modifier_callback arguments where necessary,
and changed MRO of sockercan's CyclicSendTask to
match that of the fallback.

This makes several changes to socketcan in previous commits
unnecessary. These changes are also removed.

# Conflicts:
#	can/broadcastmanager.py
#	can/bus.py
#	can/interfaces/socketcan/socketcan.py

# Conflicts:
#	can/bus.py
#	can/interfaces/socketcan/socketcan.py

# Conflicts:
#	can/interfaces/ixxat/canlib_vcinpl.py