add osmo_sockaddr_str API

For handling RTP IP addresses and ports, osmo-mgw, osmo-bsc and osmo-msc
so far have their own separate shims and code duplication around
inet_ntoa(), htons(), sockaddr conversions etc. Unify and standardize
with this common API.

In the MGW endpoint FSM that was introduced in osmo-bsc and which I
would like to re-use for osmo-msc (upcoming patch moving that to
osmo-mgw), it has turned out that using char* IP address and uint16_t
port number types are a convenient common denominator for logging,
MGCP message composition and GSM48. Ongoing osmo-msc work also uses this
for MNCC.

This is of course potentially useful for any other IP+port combinations
besides RTP stream handling.

Needless to say that most current implementations will probably stay
with their current own conversion code for a long time; for current
osmo-{bsc,msc,mgw} work (MGW endpoint FSM) though, I would like to move
to this API here.

Change-Id: Id617265337f09dfb6ddfe111ef5e578cd3dc9f63
diff --git a/include/Makefile.am b/include/Makefile.am
index 17f7d1c..6ed7fe6 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -52,6 +52,7 @@
                        osmocom/core/timer_compat.h \
                        osmocom/core/utils.h \
                        osmocom/core/write_queue.h \
+                       osmocom/core/sockaddr_str.h \
                        osmocom/crypt/auth.h \
                        osmocom/crypt/gprs_cipher.h \
 		       osmocom/ctrl/control_cmd.h \