patch 9.0.1957: termcap options should change when setting keyprotocol

Problem:  termcap options should change on keyprotocol setting
Solution: Apply termcap entries when 'keyprotocol' changes

When the 'keyprotocol' option was set after startup (including in a
user's .vimrc) the termcap entries associated with the matching protocol
were not applied. Thus, setting the option has no affect.

When 'keyprotocol' is changed it should also update the termcap entries.

closes: #13211

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Gregory Anders <greg@gpanders.com>
diff --git a/src/proto/term.pro b/src/proto/term.pro
index 4150cbe..e95befe 100644
--- a/src/proto/term.pro
+++ b/src/proto/term.pro
@@ -5,6 +5,7 @@
 void f_terminalprops(typval_T *argvars, typval_T *rettv);
 void set_color_count(int nr);
 keyprot_T match_keyprotocol(char_u *term);
+void apply_keyprotocol(char_u *term, keyprot_T prot);
 int set_termname(char_u *term);
 void free_cur_term(void);
 void getlinecol(long *cp, long *rp);