[<channel>] [<hostmask|--all>]
Unbans <hostmask> on <channel>. If <hostmask> is not given, unbans
any hostmask currently banned on <channel> that matches your current
hostmask. Especially useful for unbanning yourself when you get
unexpectedly (or accidentally) banned from the channel. <channel> is
only necessary if the message isn't sent in the channel itself.