fix init_log() called before error() call

log handler expects init_log() has been processed,
without initialization, the call results in abort.

Signed-off-by: Hiroaki KAWAI <kawai@stratosphere.co.jp>
ensure that an IPv4/IPv6 address is specified as an IPAddr object instance
ensure that a MAC address is specified as an Trema::Mac object instance
add rspec for ArpSpa action
modify argument to constructor
add Ipv4DstAddr rspec
rewording/refactoring
remove unused return statement
Merge pull request #37 from iHiroakiKawai/init_log_first

fix init_log() called before error() call