gtphub: implement restart counter properly.

Force passing a restart counter, by adding such arg to gtphub_start() (test
suite is not affected by this).

In gtphub_main.c, add -r,--restart-file <path> and next_restart_count() to
maintain the counter file. While at it, tweak the cmdline help to unify the
formatting (mostly commas and a missing line break).

Send gtphub's own restart counter. So far, the sender's restart counter was
copied through, which would break as soon as more than one GSN would talk to
the same peer with differing restart counters.

Also fix the in-mem restart counter data type (one octet, not two).

Sponsored-by: On-Waves ehi
diff --git a/openbsc/tests/gtphub/gtphub_test.c b/openbsc/tests/gtphub/gtphub_test.c
index 4181002..9ba4643 100644
--- a/openbsc/tests/gtphub/gtphub_test.c
+++ b/openbsc/tests/gtphub/gtphub_test.c
@@ -782,7 +782,7 @@
 		"00"	/* N-PDU 0 */ \
 		"00"	/* No extensions */ \
 		/* IEs */ \
-		"0e" restart /* 14: Recovery = 96 (restart counter: 1 octet) */ \
+		"0e" restart /* 14: Recovery (restart counter: 1 octet) */ \
 		"02"	/* 2 = IMSI */ \
 		  imsi	/* (8 octets) */ \
 		"0f01"	/* 15: Selection mode = MS provided APN, subscription not verified*/ \
@@ -825,7 +825,7 @@
 		  "80"	/* value = 0b10000000 = response, no rejection. */ \
 		"08"	/* 8: Reordering Required */ \
 		  "00"	/* not required. */ \
-		"0e" restart /* 14: Recovery = 1 */ \
+		"0e" restart /* 14: Recovery */ \
 		"10"	/* 16: TEI Data I */ \
 		  tei_u \
 		"11"	/* 17: TEI Control */ \
@@ -904,7 +904,7 @@
 	const char *gtp_req_to_ggsn =
 		MSG_PDP_CTX_REQ("0068",
 				"6d31",	/* mapped seq ("abcd") */
-				"60",
+				"23",
 				"42000121436587f9",
 				"00000001", /* mapped TEI Data I ("123") */
 				"00000001", /* mapped TEI Control ("321") */
@@ -938,7 +938,7 @@
 		MSG_PDP_CTX_RSP("004e",
 				"00000321", /* unmapped TEI ("001") */
 				"abcd", /* unmapped seq ("6d31") */
-				"01",
+				"23",
 				"00000002", /* mapped TEI from GGSN ("567") */
 				"00000002", /* mapped TEI from GGSN ("765") */
 				"0004""7f000101", /* gtphub's address towards SGSNs (Ctrl) */