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.h b/src/db.h
index 0064a4d..6d6723a 100644
--- a/src/db.h
+++ b/src/db.h
@@ -23,7 +23,7 @@
 };
 
 bool db_remove_reset(sqlite3_stmt *stmt);
-bool db_bind_imsi(sqlite3_stmt *stmt, const char *imsi);
+bool db_bind_text(sqlite3_stmt *stmt, const char *param_name, const char *text);
 void db_close(struct db_context *dbc);
 struct db_context *db_open(void *ctx, const char *fname);