package/squid: security bump to version 4.15

package/squid: security bump to version 4.15

Fixes the following security issues:

- CVE-2021-28651: Denial of Service in URN processing
  Due to a buffer management bug Squid is vulnerable to a Denial of service
  attack against the server it is operating on.

  This attack is limited to proxies which attempt to resolve a "urn:"
  resource identifier.  Support for this resolving is enabled by default in
  all Squid.

  https://github.com/squid-cache/squid/security/advisories/GHSA-ch36-9jhx-phm4

- CVE-2021-28652: Denial of Service issue in Cache Manager
  Due to an incorrect parser validation bug Squid is vulnerable to a Denial
  of Service attack against the Cache Manager API.

  https://github.com/squid-cache/squid/security/advisories/GHSA-m47m-9hvw-7447

- CVE-2021-28662: Denial of Service in HTTP Response Processing
  Due to an input validation bug Squid is vulnerable to a Denial of Service
  against all clients using the proxy.

  https://github.com/squid-cache/squid/security/advisories/GHSA-jjq6-mh2h-g39h

- CVE-2021-31806, CVE-2021-31807, CVE-2021-31808: Multiple Issues in HTTP
  Range header
  Due to an incorrect input validation bug Squid is vulnerable to
  a Denial of Service attack against all clients using the proxy.

  https://github.com/squid-cache/squid/security/advisories/GHSA-pxwq-f3qr-w2xf

- CVE-2021-33620: Denial of Service in HTTP Response processing
  Due to an input validation bug Squid is vulnerable to a Denial of Service
  against all clients using the proxy.

  https://github.com/squid-cache/squid/security/advisories/GHSA-572g-rvwr-6c7f

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>