This change adds support using the pjsip_tls_transport_restart
function for reloading the TLS certificate and key, if the filenames
remain unchanged. This is useful for Let's Encrypt and other
situations. Note that no restart of the transport will occur if
the certificate and key remain unchanged.
ASTERISK-30186
Change-Id: I9bc95a6bf791830a9491ad9fa43c17d4010028d0