cosmetic: refactor db_bind_imsi() as db_bind_text()

There are more uses for a generalized db_bind_text(), and in an upcoming patch
there will be similar functions like db_bind_int().

Also, add argument param_name, optionally indicating a named SQL parameter to
bind to, which will be used in subsequent patches. So far, all callers pass
NULL to yield previous db_bind_imsi() behavior of binding to the first param.

Change-Id: I87bc46a23a724677e8319d6a4b032976b7ba9394
diff --git a/src/db_hlr.c b/src/db_hlr.c
index fa962f3..3bf3912 100644
--- a/src/db_hlr.c
+++ b/src/db_hlr.c
@@ -43,7 +43,7 @@
 	sqlite3_stmt *stmt = dbc->stmt[DB_STMT_SEL_BY_IMSI];
 	int rc;
 
-	if (!db_bind_imsi(stmt, imsi))
+	if (!db_bind_text(stmt, NULL, imsi))
 		return -EINVAL;
 
 	/* execute the statement */
@@ -86,7 +86,7 @@
 		dbc->stmt[enable ? DB_STMT_SET_NAM_PS_BY_IMSI : DB_STMT_UNSET_NAM_PS_BY_IMSI];
 	int rc;
 
-	if (!db_bind_imsi(stmt, imsi))
+	if (!db_bind_text(stmt, NULL, imsi))
 		return -EINVAL;
 
 	rc = sqlite3_step(stmt); /* execute the statement */
@@ -158,7 +158,7 @@
 	else
 		stmt = dbc->stmt[DB_STMT_UPD_PURGE_CS_BY_IMSI];
 
-	if (!db_bind_imsi(stmt, imsi))
+	if (!db_bind_text(stmt, NULL, imsi))
 		return -EINVAL;
 
 	/* execute the statement */