[inets] Fix spelling and description errors in comments
[kernel] Fix doc errors in rpc:multicall example

Tiny fix of rpc:multicall example documentation. Argument order and
syntax error corrected.
[erts] Fix erlang.xml doc: badargif -> badarg if
Fix typos of "backward compatibility"

s/back(a)*ward(s)* compatibi(l)+ity/backward compatibility/g
[ssl] Fix typo in comment: keept -> kept