netfilter: fix connlimit Kconfig prompt string

Under Core Netfilter Configuration, connlimit match support has
an extra double quote at the end of it.

Fixes a portion of kernel bugzilla #52671:
  https://bugzilla.kernel.org/show_bug.cgi?id=52671



Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by:  <lailavrazda1979@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>