remote: qualify "git pull" advice for non-upstream compareBranches

remote: qualify "git pull" advice for non-upstream compareBranches

Enable ENABLE_ADVICE_PULL for push-branch comparisons too, not just
the upstream entry, so the "use git pull" hint prints when the local
branch is behind its push branch.

Spell out "git pull <remote> <branch>" so running the suggested
command actually pulls the ref the user was told about; plain
"git pull" would fetch the upstream instead.

Signed-off-by: Harald Nordgren <redacted>
Signed-off-by: Junio C Hamano <redacted>