pjproject: follow security advisories

Apply patches for CVE-2021-21375 and CVE-2020-15260 affecting
prproject. After a quick look I don't think those issues apply to
us, as GnuTLS manages the TLS part and we do resolution outside
pjsip (the daemon passes ips), but at least our pjproject will
not be affected.

Note, these patches will be removed when we bump pjproject to 2.11.

Change-Id: Ie9029f5501096c7148416cbb803a40f1c053a3d0