enable ` set tagfunc=lsp#tagfunc ` by default

[lijh8]

Hi, can set tagfunc=lsp#tagfunc be enabled by default? so we can use ctrl-], etc. in case we do not have ctags. neovim seems to do this already.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.