nfsd: add IPv6 addr escaping to fs_location hosts

The fs_location->hosts list is split on colons, but this doesn't work when
IPv6 addresses are used (they contain colons).
This patch adds the function nfsd4_encode_components_esc() to
allow the caller to specify escape characters when splitting on 'sep'.
In order to fix referrals, this patch must be used with the mountd patch
that similarly fixes IPv6 [] escaping.

Signed-off-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>