io.c: workaround for EPROTOTYPE

	* io.c (internal_write_func, internal_writev_func): retry at
	  unexpected EPROTOTYPE on macOS, to get rid of a kernel bug.
	  [ruby-core:86690] [Bug #14713]

	* ext/socket/init.c (rsock_{sendto,send,write}_blocking): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@63826 b2dd03c8-39d4-4d8f-98ff-823fe69b080e