Print IPv6 addresses with brackets in the log

[ming]

Currently IPv6 addresses are printed as is, i.e. without brackets, in various places such as:

pjsip/src/pjsua-lib/pjsua_core.c:logging_on_tx_msg, and
pjsip/src/pjsua-lib/pjsua_core.c:logging_on_rx_msg

pjsip/src/pjsua-lib/pjsua_acc.c:acc_check_nat_addr
with "IP address change detected for account"

pjsip/src/pjsua-lib/pjsua_acc.c:update_keep_alive
with "Keep-alive timer started for acc"

pjsip/src/pjsip/sip_transport_tcp.c:on_connect_complete
pjsip/src/pjsip/sip_transport_tls.c:on_connect_complete
with "transport %.*s:%d is connected to"

For clarity, it is desirable for these addresses to be printed with the brackets, especially if there's a port number behind it.

In the SIP message itself, we have implemented this by adding beginquote and endquote, such as in
pjsua_acc.c: acc_check_nat_addr(), pjsua_acc_create_uac_contact(), pjsua_acc_create_uas_contact()

So we probably need to create a helper new pjlib API instead of copy-pasting it all over the place.